Atp Oil & Gas 424B5 Prospectus supplement for primary offering

Filed pursuant to Rule 424(b)(5)

A filing fee of $8,297, calculated in accordance with

Rule 457(r), has been transmitted to the SEC in connection

with the securities offered from the registration statement

(File No. 333-146588) by means of this prospectus supplement

Prospectus Supplement

(To prospectus dated November 14, 2007)

5,000,000 Shares

LOGO

Common Stock

We are offering 5,000,000 shares of our common stock.

Our common stock is quoted on The NASDAQ Global Select Market under the symbol “ATPG.” On November 14, 2007, the last reported sale price of our common stock on The NASDAQ Global Select Market was $52.29 per share.

Investing in our common stock involves risk. See “Risk Factors” included in the accompanying prospectus for a description of the various risks you should consider in evaluating an investment in the shares.


	Public Offering Price		Underwriting Discount		Proceeds to Us (Before Expenses)
Per Share	$	47.00	$	1.645	$	45.355
Total	$	235,000,000	$	8,225,000	$	226,775,000

The selling shareholder has granted the underwriters a 30-day option to purchase up to an additional 750,000 shares from him at a price of $47.00 per share solely to cover any over-allotments. The selling shareholder is a member of our senior management. See “Selling Shareholder” on page S-5 of this prospectus supplement. We will not receive any proceeds from the sale of shares of our common stock by the selling shareholder.

Delivery of the shares of common stock is expected to be made on or about November 20, 2007.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.


Howard Weil Incorporated		Johnson Rice & Company L.L.C.

Joint Book-Running Managers

The date of this prospectus supplement is November 15, 2007.

TABLE OF CONTENTS


		Page
Prospectus Supplement
About This Prospectus Supplement and the Prospectus		S-ii
Summary		S-1
A Warning About Forward-Looking Statements		S-3
Use of Proceeds		S-3
Price Range of Common Stock		S-4
Selling Shareholder		S-5
Underwriting		S-5
Legal Matters		S-7

Prospectus
About This Prospectus		i
A Warning About Forward-Looking Statements		ii
Where You Can Find More Information		ii
Incorporation by Reference		ii
About the Company		1
Risk Factors		2
Use of Proceeds		9
Selling Shareholders		9
The Securities We or the Selling Shareholders May Offer		9
Description of Capital Stock		10
Description of Warrants		13
Legal Ownership of Securities		15
Plan of Distribution		17
Legal Matters		18
Experts		19

S-i

ABOUT THIS PROSPECTUS SUPPLEMENT AND THE PROSPECTUS

This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering. The second part, the accompanying prospectus, gives more general information, some of which may not apply to this offering. You should read the entire prospectus supplement, as well as the accompanying prospectus and the documents incorporated by reference that are described under “Where You Can Find More Information” and “Incorporation by Reference” in the accompanying prospectus. In the event that the description of the offering varies between this prospectus supplement and the accompanying prospectus, you should rely on the information contained in this prospectus supplement.

You should rely only on the information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus. We have not, the selling shareholder has not and the underwriters have not authorized any other person to provide you with additional or different information. If anyone provides you with additional, different or inconsistent information, you should not rely on it. We are not, the selling shareholder is not and the underwriters are not making any offer to sell these securities in any jurisdiction where the offer to sell is not permitted. You should not assume that the information we have included in this prospectus supplement and the accompanying prospectus is accurate as of any date other than the date hereof or thereof respectively, or that information we have incorporated by reference is accurate as of any date other than the date of the document incorporated by reference. Our business, financial condition, results of operations and prospects may have changed since those dates.

Unless the context indicates otherwise, all references in this prospectus supplement to “we,” “our,” “us,” or the “company” refer to ATP Oil & Gas Corporation and its subsidiaries on a consolidated basis, unless otherwise indicated or the context otherwise requires.

S-ii

SUMMARY

The Company

ATP Oil & Gas Corporation was incorporated in Texas in 1991. We are engaged in the acquisition, development and production of oil and natural gas properties in the Gulf of Mexico and the U.K. and Dutch Sectors of the North Sea (the “North Sea”). We primarily focus our efforts on oil and natural gas properties where previous drilling has encountered reservoirs that appear to contain commercially productive quantities of oil and gas. Many of these properties contain proved undeveloped reserves that are economically attractive to us but are not strategic to major or exploration-oriented independent oil and natural gas companies. Occasionally we will acquire properties that are already producing or where previous drilling has encountered reservoirs that appear to us to contain commercially productive quantities of oil and gas even though the reservoirs do not meet the SEC definition of proved reserves. Our management team has extensive engineering, geological, geophysical, technical and operational expertise in successfully developing and operating properties in both our current and planned areas of operation.

At December 31, 2006, we had estimated net proved reserves of 636.9 Bcfe, of which approximately 359.4 Bcfe (56%) was in the Gulf of Mexico and 277.5 Bcfe (44%) was in the North Sea. Year-end reserves were comprised of 329.2 Bcf of natural gas (52%) and 51.3 MMBbls of oil (48%). The majority of our oil reserves (66%) are located in the Gulf of Mexico, with the balance located in the North Sea. The majority of our natural gas reserves (52%) are located in the North Sea, with the balance located in the Gulf of Mexico. Of our total proved reserves, 129.6 Bcfe (20%) were producing, 84.3 Bcfe (13%) were developed and not producing and 423.0 Bcfe (66%) were undeveloped. The estimated pre-tax PV-10 of our proved reserves at December 31, 2006 was $1.3 billion and the standardized measure of discounted future net cash flows at December 31, 2006 was $1 billion. See “Item 2. Properties – Oil and Natural Gas Reserves” in our Annual Report on Form 10-K for the year ended December 31, 2006, which is incorporated herein by reference, for a reconciliation to after-tax PV-10. See “Incorporation by Reference.”

At December 31, 2006, we had leasehold and other interests in 72 offshore blocks, 44 platforms and 112 wells, including 14 subsea wells, in the Gulf of Mexico. We operated 94 (84%) of these wells, including all of the subsea wells, and 86% of our offshore platforms. We also had interests in 11 blocks and 2 company-operated subsea wells in the North Sea. Our average working interest in our properties at December 31, 2006 was approximately 81%. For more information regarding our operations and assets in the Gulf of Mexico and North Sea, see Note 14, “Segment Information,” to the Notes to Consolidated Financial Statements in our Annual Report on Form 10-K for the year ended December 31, 2006, which is incorporated herein by reference. See “Incorporation by Reference.”

Our principal offices are located at 4600 Post Oak Place, Suite 200, Houston, Texas 77027, where our telephone number is (713) 622-3311.

A detailed discussion of our business is included in our Annual Report on Form 10-K for the fiscal year ended December 31, 2006 and our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2007, June 30, 2007 and September 30, 2007, all of which are incorporated herein by reference. See “Incorporation by Reference.”

S-1

The Offering

Common stock offered by us

5,000,000 shares

Common stock to be outstanding after this offering

35,632,351 shares(1)

Over-allotment option granted by selling shareholder

Up to 750,000 shares. See “Selling Shareholder” and “Underwriting.”

Use of proceeds

We estimate that we will receive net proceeds from this offering of approximately $226 million after deducting underwriting discounts and commissions and estimated offering expenses. We are required to offer to our lenders approximately $56 million (or 25%) of the net proceeds from this offering to prepay outstanding indebtedness under our Third Amended and Restated Credit Agreement dated December 28, 2006, as amended by Amendment No. 1 and Agreement dated March 23, 2007, with Credit Suisse, as administrative agent for the lenders. We intend to use the remaining net proceeds from this offering to fund capital expenditures related to our drilling and development activities, including a potential second MinDOC at our Telemark Hub and potential new wells at Wenlock, Canyon Express Hub and Green Canyon 37, and for general corporate purposes. We will not receive any of the proceeds from the sale of common stock by the selling shareholder if the underwriters exercise the over-allotment option. See “Use of Proceeds.”

NASDAQ Global Select Market symbol

“ATPG”

Dividend policy

We currently anticipate that we will retain all future earnings, if any, to finance the growth and development of our business. We do not intend to pay cash dividends in the foreseeable future. In addition, our existing credit facilities limit our ability to pay dividends and make other distributions.

Risk factors

We are subject to a number of risks that you should carefully consider before deciding to invest in our common stock. These risks are discussed more fully in “Risk Factors” included in the accompanying prospectus.

(1) The number of shares of common stock outstanding after the offering is based on 30,632,351 shares of common stock outstanding as of November 14, 2007, excluding shares issuable upon the exercise of outstanding stock options awarded under our 2000 Stock Plan and held by our employees, executive officers and directors.

S-2

A WARNING ABOUT FORWARD-LOOKING STATEMENTS

This prospectus supplement (and other documents to which it refers) contains statements about future events and expectations which are characterized as forward-looking statements. Words such as “may”, “could”, “would”, “should”, “believes”, “expects”, “anticipates”, “estimates”, “intends”, “plans”, “targets”, “objectives”, “seek”, “strive”, negatives of these words and similar expressions are intended to identify forward-looking statements. Forward-looking statements are based on management’s beliefs, assumptions and expectations of our future economic performance, taking into account the information currently available to our management. They are expressions based on historical fact, but do not guarantee future performance. Forward-looking statements involve risks, uncertainties and assumptions and certain other factors that may cause our actual results, performance or financial condition to differ materially from the expectations of future results, performance or financial condition we express or imply in any forward-looking statements. Factors that could contribute to these differences include those discussed in “Risk Factors” in the accompanying prospectus. We qualify any forward-looking statements entirely by these cautionary factors.

We believe these forward-looking statements are reasonable, but we caution that you should not place undue reliance on these forward-looking statements, because our future results and shareholder value may differ materially from those expressed or implied by these forward-looking statements. We do not intend to update any forward-looking statement, whether written or oral, relating to the matters discussed in this prospectus supplement.

USE OF PROCEEDS

We expect the net proceeds from this offering to be approximately $226 million, after deducting underwriters’ discounts and the estimated expenses of the offering.

Under the terms of our Third Amended and Restated Credit Agreement dated December 28, 2006, as amended by Amendment No. 1 and Agreement dated March 23, 2007 (such date, the “Amendment Date,” and the Third Amended and Restated Credit Agreement as amended, the “Credit Agreement”), with Credit Suisse, as administrative agent for the lenders, we are required to offer approximately $56 million (or 25%) of the net proceeds from this offering to our lenders to prepay term loans under the Credit Agreement. Each lender has the right to reject its share of the mandatory prepayment, and any declined proceeds must then be reoffered to those lenders that have accepted their share of the mandatory prepayment; we may retain any remaining declined proceeds. As of the Amendment Date, we borrowed additional amounts in the aggregate principal amount of $375.0 million, all of the proceeds of which were used by us (i) to pay fees and expenses incurred in connection with the Credit Agreement in an aggregate amount of $8.4 million, (ii) to repay in full all outstanding borrowings under the then-existing second lien term loan facility, which had an original face amount of $175.0 million and bore interest at a rate of LIBOR plus 4.75%, and (c) from time to time solely for general corporate purposes, including for the development of the properties acquired to-date in 2007. The effective interest rate in respect of the Credit Agreement term loans was 9.49% per annum as of September 30, 2007, and the maturity date for this indebtedness is April 14, 2010.

We intend to use the remaining net proceeds from this offering to fund capital expenditures related to our drilling and development activities, including a potential second MinDOC at our Telemark Hub and potential new wells at Wenlock, Canyon Express Hub and Green Canyon 37, and for general corporate purposes. We will not receive any of the proceeds from the sale of common stock by the selling shareholder if the underwriters exercise the over-allotment option. See “Selling Shareholder.”

S-3

PRICE RANGE OF COMMON STOCK

Our common stock is listed and traded on The NASDAQ Global Select Market under the symbol “ATPG.” The following table includes the high and low sales prices for our common stock as reported on The NASDAQ Global Select Market for the periods presented.


	Price Range of Common Stock
	High		Low
2007
Fourth Quarter (through November 14, 2007)	$	57.58	$	46.66
Third Quarter		49.39		38.44
Second Quarter		49.00		37.46
First Quarter		43.65		35.15

2006
Fourth Quarter	$	47.29	$	34.16
Third Quarter		43.30		35.35
Second Quarter		49.70		35.04
First Quarter		44.05		36.05

2005
Fourth Quarter	$	39.20	$	27.91
Third Quarter		34.00		23.51
Second Quarter		24.62		17.86
First Quarter		26.55		16.76

The closing price of our common stock on The NASDAQ Global Select Market on November 14, 2007 was $52.29.

S-4

SELLING SHAREHOLDER

A total of 750,000 shares of common stock are to be sold by the selling shareholder if the underwriters exercise the over-allotment option in full. The selling shareholder, T. Paul Bulmahn, is our founder, Chairman and President. The following table provides information about the selling shareholder, including:

•

the number and percentage of outstanding shares the selling shareholder owns prior to the offering, as of November 14, 2007; and

•

the number and percentage of outstanding shares the selling shareholder will own after the offering, assuming exercise of the underwriters’ over-allotment option in full.

Based on SEC reports, prior to the offering Mr. Bulmahn is, and assuming the exercise of the underwriters’ over-allotment option in full, after the offering will be, the owner of record of the largest percentage of the company’s outstanding common stock. We will not receive any of the proceeds from the sale of common stock by the selling shareholder.


	Beneficial Ownership Prior to Offering			Shares Offered Pursuant to Over-allotment Option	Beneficial Ownership After Offering (Assuming Full Exercise of Over-allotment Option)
Name	Number(2)	Percentage(1)		Shares Offered Pursuant to Over-allotment Option	Number	Percentage(1)
T. Paul Bulmahn	7,030,474	23.0	%	750,000	6,280,474	17.6	%

(1)	Includes beneficial ownership of 94,104 restricted shares of common stock.

(2)	See “Risk Factors—Members of our management team own a significant amount of common stock giving them influence or control in corporate transactions and other matters, and the interests of these individuals could differ from those of our other stockholders” included in the accompanying prospectus.

UNDERWRITING

Howard Weil Incorporated and Johnson Rice & Company L.L.C. are acting as the underwriters for the offering. Subject to the terms and conditions stated in the underwriting agreement, dated the date of this prospectus supplement, each of the underwriters named below has severally agreed to purchase from us, and we have agreed to sell to the underwriters, the respective number of shares of common stock shown opposite its name below:


Underwriter		Number of Shares
Howard Weil Incorporated		2,500,000
Johnson Rice & Company L.L.C.		2,500,000

Total		5,000,000

The underwriting agreement provides that the underwriters’ obligation to purchase shares of our common stock is subject to approval of legal matters by counsel and the satisfaction of the conditions contained in the underwriting agreement. The conditions contained in the underwriting agreement include the condition that the representations and warranties made by us to the underwriters are true, that there has been no material adverse change to our condition or in the financial markets and that we deliver to the underwriters customary closing documents. The underwriters are obligated to purchase all of the shares of common stock (other than those covered by the over-allotment option described below) if they purchase any of the shares.

S-5

The underwriters propose to offer the shares of common stock to the public at the public offering price set forth on the cover page of this prospectus supplement. The underwriters may offer the common stock to securities dealers at the price to the public less a concession not in excess of $0.99 per share. After the shares of common stock are released for sale to the public, the underwriter may vary the offering price and other selling terms from time to time.

The selling shareholder has granted to the underwriters an option, exercisable for 30 days from the date of the underwriting agreement, to purchase up to 750,000 additional shares at the public offering price per share less the underwriting discount shown on the cover page of this prospectus supplement. The underwriters may exercise this option solely to cover over-allotments, if any, made in connection with this offering.

The following table summarizes the compensation to be paid to the underwriters by us and the selling shareholder, assuming the underwriters’ over-allotment option is fully exercised, in connection with this offering.


			Total
	Per share		Without over-allotment		With over-allotment
Public offering price by us	$	47.00	$	235,000,000	$	235,000,000
Underwriting fees to be paid by us	$	1.645	$	8,225,000	$	8,225,000
Proceeds, before expenses, to us	$	45.355	$	226,775,000	$	226,775,000
Public offering price by the selling shareholder	$	47.00	$	0.00	$	35,250,000
Underwriting fees to be paid by the selling shareholder	$	1.645	$	0.00	$	1,233,750
Proceeds, before expenses, to the selling shareholder	$	45.355	$	0.00	$	34,016,250

We estimate our expenses associated with the offering, excluding underwriting discounts and commissions, will be approximately $775,000.

We and the selling shareholder have agreed to indemnify the underwriters against certain liabilities, including liabilities under the federal securities laws, or to contribute to payments that may be required to be made in respect of these liabilities.

We and our officers and directors have agreed that, for a period of 90 days from the date of this prospectus supplement, we and they will not, without the prior written consent of the underwriters, directly or indirectly, offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of any share of common stock or any securities convertible into or exercisable or exchangeable for common stock, or file any registration statement under the Securities Act with respect to any of the foregoing or enter into any swap or any other agreement or transaction that transfers, in whole or in part, directly or indirectly, the economic consequence of ownership of the common stock, except for the sale to the underwriters in this offering, the issuance by us of any securities or options to purchase common stock under existing, amended or new employee benefit plans maintained by us and the filing of or amendment to any registration statement related to the foregoing, the issuance by us of securities in exchange for or upon conversion of our outstanding securities described herein, the filing of or an amendment to any registration statement pursuant to registration rights held by third parties not subject to a lock-up agreement, or certain transfers in the case of officers or directors (i) in the form of bona fide gifts, intra family transfers and transfers related to estate planning matters or (ii) for all officers and directors other than Mr. Bulmahn, who has agreed that he will sell shares during such 90-day period only in connection with the over-allotment option, not more than 250,000 shares in the aggregate. The underwriters have advised us that it does not have any present intent to release the lock-up agreements prior to the expiration of the applicable restricted period.

S-6

The underwriters may engage in over-allotment, stabilizing transactions, syndicate covering transactions, penalty bids and passive market making in accordance with Regulation M under the Exchange Act. Over-allotment involves syndicate sales in excess of the offering size, which creates a syndicate short position. Covered short sales are sales made in an amount not greater than the number of shares available for purchase by the underwriters under their over-allotment option. The underwriters may close out a covered short sale by exercising its over-allotment option or purchasing shares in the open market. Naked short sales are sales made in an amount in excess of the number of shares available under the over-allotment option. The underwriters must close out any naked short sale by purchasing shares in the open market. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Syndicate covering transactions involve purchases of the shares of common stock in the open market after the distribution has been completed in order to cover syndicate short positions. Penalty bids permit the underwriters to reclaim a selling concession from a syndicate member when the shares of common stock originally sold by such syndicate member is purchased in a syndicate covering transaction to cover syndicate short positions. Penalty bids may have the effect of deterring syndicate members from selling to people who have a history of quickly selling their shares. In passive market making, market makers in the shares of common stock who are underwriters or prospective underwriters may, subject to certain limitations, make bids for or purchases of the shares of common stock until the time, if any, at which a stabilizing bid is made. These stabilizing transactions, syndicate covering transactions and penalty bids may cause the price of the shares of common stock to be higher than it would otherwise be in the absence of these transactions. The underwriters are not required to engage in these activities, and may end any of these activities at any time.

LEGAL MATTERS

The validity of shares of common stock offered by this prospectus supplement will be passed upon for us by Jackson Walker L.L.P., Houston, Texas. Certain legal matters will be passed on for the underwriters by Porter & Hedges, L.L.P.

S-7

PROSPECTUS

LOGO

Common Stock

Preferred Stock

Depositary Shares

Warrants

We may from time to time offer to sell common stock, preferred stock, depositary shares or warrants. In addition, our selling shareholders may from time to time offer to sell common stock. Each time we or our selling shareholders sell securities pursuant to this prospectus, we will provide a new prospectus or a supplement to this prospectus that contains specific information about the offering and the specific terms of the securities offered. You should read this prospectus and any other applicable prospectus or prospectus supplement carefully before you invest in our securities.

This prospectus may not be used to sell securities unless it is accompanied by a prospectus supplement that contains a description of those securities.

Our common stock is quoted on The NASDAQ Global Select Market under the symbol “ATPG.”

Investing in our common stock involves risk. See “Risk Factors” beginning on page 2 of the accompanying prospectus for a description of the various risks you should consider in evaluating an investment in the shares.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined that this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is November 14, 2007.

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, using a “shelf” registration process. Under this shelf process, we or the selling shareholders may from time to time offer to sell securities in one or more offerings. Each time we or the selling shareholders sell securities pursuant to this prospectus, we or the selling shareholders, as applicable, will provide a prospectus or a supplement to this prospectus that contains specific information about the offering. You should read this prospectus and any other applicable prospectus or prospectus supplement carefully before you invest in our securities.

Unless the context indicates otherwise, all references in this prospectus to “we,” “our,” “us,” or “the company” refer to ATP Oil & Gas Corporation and its subsidiaries on a consolidated basis, unless otherwise indicated or the context otherwise requires.

TABLE OF CONTENTS


		Page
About this Prospectus		i

A Warning About Forward-Looking Statements		ii

Where You Can Find More Information		ii

Incorporation by Reference		ii

About the Company		1

Risk Factors		2

Use of Proceeds		9

Selling Shareholders		9

The Securities We or the Selling Shareholders May Offer		9

Description of Capital Stock		10

Description of Warrants		13

Legal Ownership of Securities		15

Plan of Distribution		17

Legal Matters		18

Experts		19

You should rely only on the information contained or incorporated by reference in this prospectus or the documents to which we have referred you or information that is contained in any free writing prospectus we may authorize to be delivered to you. We have not authorized anyone to provide you with information that is different from such information. If anyone provides you with different information, you should not rely on it. We have not authorized anyone to provide you with different information. The information contained in this prospectus is accurate only as of the date of each document regardless of the time of delivery of this prospectus or any sale of these securities. In case there are any differences or inconsistencies between this prospectus and the information incorporated by reference, you should rely on the information in the document with the latest date.

A WARNING ABOUT FORWARD-LOOKING STATEMENTS

This prospectus and any prospectus supplement (and other documents to which each refers) contain statements about future events and expectations which are characterized as forward-looking statements. Words such as “may”, “could”, “would”, “should”, “believes”, “expects”, “anticipates”, “estimates”, “intends”, “plans”, “targets”, “objectives”, “seek”, “strive”, negatives of these words and similar expressions are intended to identify forward-looking statements. Forward-looking statements are based on management’s beliefs, assumptions and expectations of our future economic performance, taking into account the information currently available to our management. They are expressions based on historical fact, but do not guarantee future performance. Forward-looking statements involve risks, uncertainties and assumptions and certain other factors that may cause our actual results, performance or financial condition to differ materially from the expectations of future results, performance or financial condition we express or imply in any forward-looking statements. Factors that could contribute to these differences include those discussed in “Risk Factors” in this prospectus. We qualify any forward-looking statements entirely by these cautionary factors.

We believe these forward-looking statements are reasonable, but we caution that you should not place undue reliance on these forward-looking statements, because our future results and shareholder values may differ materially from those expressed or implied by these forward-looking statements. We do not intend to update any forward-looking statement, whether written or oral, relating to the matters discussed in this prospectus.

WHERE YOU CAN FIND MORE INFORMATION

We are subject to the information requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), which means that we are required to file reports, proxy statements, and other information, all of which are available for review and copying at the Public Reference Room of the Securities and Exchange Commission, 100 F. Street, NE, Washington, D.C. 20549. You may obtain information on the operation of the Public Reference Room, by calling the SEC at 1-800-SEC-0330. The SEC maintains an Internet website at http://www.sec.gov where you can access reports, proxy, information and registration statements, and other information regarding registrants that file electronically with the SEC through the EDGAR system.

We have filed a registration statement on Form S-3 to register the securities to be issued pursuant to this prospectus. As allowed by SEC rules, this prospectus does not contain all of the information you can find in the registration statement or the exhibits to the registration statement because some parts of the registration statement are omitted in accordance with the rules and regulations of the SEC. You may obtain a copy of the registration statement from the SEC at the address listed above or from the SEC’s website.

We also maintain an Internet website at http://www.atpog.com, which provides additional information about our company through which you can also access our SEC filings. The information set forth on our website is not part of this prospectus.

INCORPORATION BY REFERENCE

This prospectus incorporates important business and financial information about us which is not included in or delivered with this prospectus. The information in the documents incorporated by reference is considered to be part of this prospectus. Statements contained in documents that we file with the SEC and that are incorporated by reference in this prospectus automatically update and supersede information contained in this prospectus, including information in previously filed documents or reports that have been incorporated by reference in this prospectus, to the extent the new information differs from or is inconsistent with the old information. The following documents filed by us under the Exchange Act are incorporated by reference into this prospectus as of their respective dates of filing:

•

our Annual Report on Form 10-K for the year ended December 31, 2006, including information incorporated by reference from our Proxy Statement on Schedule 14A for the 2007 Annual Meeting of Shareholders;

•

our Quarterly Reports Form 10-Q for the quarters ended March 31, 2007, June 30, 2007 and September 30, 2007;

•

our Current Reports Form 8-K filed with the SEC on March 23, 2007, September 7, 2007 and September 14, 2007; and

•

all documents filed after the date of this prospectus pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (other than those furnished pursuant to Item 2.02 or Item 7.01 of Form 8-K, unless otherwise stated therein).

Documents incorporated by reference are available from us without charge, excluding all exhibits, unless an exhibit has been specifically incorporated by reference in this prospectus. You may obtain documents incorporated by reference in this prospectus by requesting them in writing, by telephone, by facsimile or by e-mail from Albert L. Reese, Jr., Chief Financial Officer, ATP Oil & Gas Corporation, at 4600 Post Oak Place, Suite 200, Houston, Texas 77027; telephone number (713) 622-3311; facsimile number (713) 622-5101; e-mail address areese@atpog.com.

ABOUT THE COMPANY

Our principal offices are located at 4600 Post Oak Place, Suite 200, Houston, Texas 77027, where our telephone number is (713) 622-3311.

RISK FACTORS

Investment in our securities involves a high degree of risk. You should carefully consider the following risk factors in addition to the other information included or incorporated by reference in this prospectus. Each of these risk factors could adversely affect our business, operating results and financial condition, as well as adversely affect the value of an investment in our common stock or other securities.

Our actual development results are likely to differ from our estimates of our proved reserves. We may experience production that is less than estimated and development costs that are greater than estimated in our reserve reports. Such differences may be material.

Estimates of our oil and natural gas reserves and the costs and timing associated with developing these reserves may not be accurate. Additionally, approximately 66% of our total proved reserves are undeveloped. Development of these reserves may not yield the expected results, or the development may be delayed or the development costs may exceed our estimates, any of which may materially affect our financial position and results of operations. Development activity may result in downward adjustments in reserves or higher than estimated costs.

Our estimates of our proved oil and natural gas reserves and the estimated future net revenues from such reserves are based upon various assumptions, including assumptions required by the SEC relating to oil and natural gas prices, drilling and operating expenses, capital expenditures, taxes and availability of funds. This process requires significant decisions and assumptions in the evaluation of available geological, geophysical, engineering and economic data for each reservoir. Therefore, these estimates are inherently imprecise and the quality and reliability of this data can vary.

Any significant variance could materially affect the estimated quantities and PV-10 value of our reserves. Our properties may also be susceptible to hydrocarbon drainage from production by other operators on adjacent properties. In addition, we will likely adjust estimates of proved reserves to reflect production history, results of development, prevailing oil and natural gas prices and other factors, many of which are beyond our control. Actual production, revenues, taxes, development expenditures and operating expenses with respect to our reserves may vary materially from our estimates.

Delays in the development of or production curtailment at our material properties may adversely affect our financial position and results of operations.

The size of our operations and our capital expenditure budget limits the number of properties that we can develop in any given year. Complications in the development of any single material well may result in a material adverse effect on our financial condition and results of operations. For instance, during 2006, we experienced production delays and increased development costs in connection with the development of our Tors wells in the North Sea. In late 2005, we experienced delays and increased development costs in developing our Gomez project in the Gulf of Mexico as a result of hurricanes Katrina and Rita.

In addition, a relatively few number of wells contribute to a substantial portion of our production. If we were to experience operational problems resulting in the curtailment of production in any of these wells, our total production levels would be adversely affected, which would have a material adverse effect on our financial condition and results of operations.

The unavailability or increased cost of drilling rigs, equipment, supplies, personnel and oilfield services could adversely affect our ability to execute on a timely basis our development plans within our budget.

Shortages or an increase in cost of drilling rigs, equipment, supplies or personnel could delay or adversely affect our operations, which could have a material adverse effect on our business, financial condition and results of operations. In periods of increased drilling activity in the Gulf of Mexico and the North Sea, we may experience increases in associated costs, including those related to drilling rigs, equipment, supplies and personnel and the services and products of other vendors to the industry. Increased drilling activity in the Gulf of Mexico and the North Sea also decreases the availability of offshore rigs and associated equipment. These costs may increase further and necessary equipment and services may not be available to us at economical prices.

If we are not able to generate sufficient funds from our operations and other financing sources, we may not be able to finance our planned development activity, acquisitions or service our debt.

We have historically needed and will continue to need substantial amounts of cash to fund our capital expenditure and working capital requirements. Our ongoing capital requirements consist primarily of funding acquisition, development and abandonment of oil and gas reserves and to meet our debt service obligations. Cash paid for capital expenditures for oil and gas properties was approximately $585.5 million, $420.5 million and $87.4 million for the years ended December 31, 2006, 2005 and 2004, respectively. Because we have experienced a negative working capital position in past years, we have been dependent on debt and equity financing to meet our working capital requirements that were not funded from operations.

For 2007, we plan to finance anticipated expenses, debt service and acquisition and development requirements with available cash, funds generated from cash provided by operating activities and net cash proceeds from the potential sale of assets, issuance of debt or new equity offerings. If these anticipated funds are less than our requirements, we may have to forego or reduce our capital program.

Low commodity prices, production problems, disappointing drilling results and other factors beyond our control could reduce our funds from operations and may restrict our ability to obtain additional financing. Furthermore, we have incurred losses in the past that may affect our ability to obtain financing. In addition, financing may not be available to us in the future on acceptable terms or at all. In the event additional capital is not available, we may curtail our acquisition, drilling, development and other activities or be forced to sell some of our assets on an untimely or unfavorable basis. In addition, we may not be able to pay interest and principal on our debt obligations.

Oil and natural gas prices are volatile, and low prices have had in the past and could have in the future a material adverse impact on our business.

Our revenues, profitability and future growth and the carrying value of our properties depend substantially on the prices we realize for our oil and natural gas production. Our realized prices also affect the amount of cash flow available for capital expenditures and our ability to borrow and raise additional capital.

Historically, the markets for oil and natural gas have been volatile, and they are likely to continue to be volatile in the future. For example, oil and natural gas prices increased significantly in late 2000 and early 2001 and then steadily declined in 2001, only to climb again in recent years to near all-time highs before declining again in late 2006. Among the factors that can cause this volatility are:

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worldwide or regional demand for energy, which is affected by economic conditions;

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the domestic and foreign supply of oil and natural gas;

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weather conditions;

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domestic and foreign governmental regulations;

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political conditions in natural gas or oil producing regions;

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the ability of members of the Organization of Petroleum Exporting Countries to agree upon and maintain oil prices and production levels; and

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price and availability of alternative fuels.

It is impossible to predict oil and natural gas price movements with certainty. Lower oil and natural gas prices may not only decrease our revenues on a per-unit basis but also may reduce the amount of oil and natural gas that we can produce economically. A substantial or extended decline in oil and natural gas prices may materially and adversely affect our future business, financial condition, results of operations, liquidity and ability to finance planned capital expenditures. Further, oil prices and natural gas prices do not necessarily move together.

Our price risk management decisions may reduce our potential gains from increases in commodity prices and may result in losses.

As required by our lenders, we periodically utilize financial derivative instruments and fixed price forward sales contracts with respect to a portion of our expected production, generally not less than 40% or more than 80% of such production. These instruments expose us to risk of financial loss if:

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production is less than expected for forward sales contracts;

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the counterparty to the derivative instrument defaults on its contract obligations; or

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there is an adverse change in the expected differential between the underlying price in the financial derivative instrument and the fixed price forward sales contract and actual prices received.

Our results of operations may be negatively impacted in the future by our financial derivative instruments and fixed price forward sales contracts—our fixed forward sales are designated as normal sales under derivative accounting rules—and these instruments may limit any benefit we would receive from increases in the prices for oil and natural gas. For the years ended December 31, 2006, 2005 and 2004, we realized a loss on settled financial derivatives of $3.2 million, $0.7 million and $1.2 million, respectively.

Our debt instruments impose restrictions on us that may affect our ability to successfully operate our business.

In March 2007, we amended our Third Amended and Restated Credit Agreement, dated December 28, 2006 (as amended, the “Credit Agreement”), which amended and restated the Second Amended and Restated Credit Agreement dated June 22, 2006 and all prior amendments thereto. The Credit Agreement provides for aggregate outstanding borrowings of $1.275 billion (the “Term Loans”) and up to $50.0 million under a Senior Secured Revolving Credit Facility (the “Revolver”). The Term Loans mature in April 2010. The Revolver matures in October 2009. The Term Loans and the

Revolver are secured by substantially all of our oil and gas assets in the Gulf of Mexico and a pledge of 65% of the capital stock of our subsidiaries, ATP Oil & Gas (UK), Limited and ATP Oil & Gas (Netherlands) B.V., and are guaranteed by our wholly owned subsidiary, ATP Energy, Inc. As of November 13, 2007, we had an aggregate $1.262 billion principal outstanding under the Term Loans, and no amounts outstanding under the Revolver. The Term Loans contain customary restrictions, including covenants limiting our ability to incur additional debt, grant liens, make investments, consolidate, merge or acquire other businesses, sell assets, pay dividends and other distributions and enter into transactions with affiliates. We also must maintain specified financial requirements under the terms of our Term Loans and the Revolver including the following, as defined in the Credit Agreement:

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Minimum Current Ratio of 1.0 to 1.0;

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Ratio of Total Net Debt to Consolidated EBITDAX of not greater than 3.0 to 1.0 at the end of each quarter;

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Ratio of Consolidated EBITDAX to Consolidated Interest Expense of not less than 2.5 to 1.0 for any four consecutive fiscal quarters;

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Ratio of pre-tax PV-10 of our total Proved Developed Producing oil and gas reserves to Net Debt of at least 0.5 to 1.0 at September 30 and December 31 of any fiscal year;

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Ratio of pre-tax PV-10 of our Total Proved oil and gas reserves plus 50% of our pre-tax probable oil and gas reserves, both adjusted for current oil and gas price estimates, to Net Debt of at least 3.0 to 1.0 at September 30 or December 31 of any fiscal year;

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Commodity Hedging Agreements, based on forecasted production attributable to our proved producing reserves and calculated on a twelve rolling month basis, of (i) not less than 60% during the year subsequent to measurement, and (ii) not less than 40% during the second year subsequent to measurement;

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limit during any fiscal year Permitted Business Investments, as defined, to $150.0 million or 7.5% of PV-10 value of our total proved reserves.

In September 2007, we entered into an Unsecured Subordinated Credit Agreement (the “Subordinated Notes”) with Credit Suisse (as Administrative Agent for the lenders) and the lenders named therein for aggregate borrowings of $210.0 million. The Subordinated Notes mature in September 2011. Such borrowings are subordinated to the borrowings under the Credit Agreement and may be prepaid at any time at the option of the company, subject to limitations set forth in the Credit Agreement. The Subordinated Notes contain no financial performance covenants, but contain customary restrictions like those negative covenants listed above for the Term Loans.

These restrictions may make it difficult for us to successfully execute our business strategy or to compete in our industry with companies not similarly restricted. While we were in compliance with all of the financial covenants applicable to our Term Loans at December 31, 2006, 2005 and 2004, during 2003 and in February 2004, we were required to obtain waivers for certain of our financial covenants in our prior credit facility. If we are unable to meet the requirements of our Term Loans and Subordinated Notes or any new financial transaction that we may enter into, we may be required to seek waivers from our lenders and there is no assurance that such waivers would be granted.

We have debt, trade payables and related interest payment requirements that may restrict our future operations and impair our ability to meet our obligations.

Our debt, trade payables, and related interest payment requirements may have important consequences. For instance, they could:

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make it more difficult or render us unable to satisfy these or our other financial obligations;

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require us to dedicate a substantial portion of any cash flow from operations to the payment of interest and principal due under our debt, which will reduce funds available for other business purposes;

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increase our vulnerability to general adverse economic and industry conditions;

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limit our flexibility in planning for, or reacting to, changes in our business and the industry in which we operate;

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place us at a competitive disadvantage compared to some of our competitors that have less financial leverage; and

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limit our ability to obtain additional financing required to fund working capital and capital expenditures and for other general corporate purposes.

Our ability to satisfy our obligations and to reduce our total debt depends on our future operating performance and on economic, financial, competitive and other factors, many of which are beyond our control. We cannot provide assurance that our business will generate sufficient cash flow or that future financings will be available to provide sufficient proceeds to meet these obligations. The successful execution of our business strategy and the maintenance of our economic viability are also contingent upon our ability to meet our financial obligations.

Our Gulf of Mexico properties are subject to rapid production declines. Therefore, we are required to replace our reserves at a faster rate than companies whose onshore reserves have longer production periods. We may not be able to identify or complete the acquisition of properties with sufficient proved reserves to implement our business strategy.

Production of reserves from reservoirs in the Gulf of Mexico generally declines more rapidly than production from reservoirs in many other producing regions of the world. While this results in recovery of a relatively higher percentage of reserves from properties in the Gulf of Mexico during the initial years of production, we must incur significant capital expenditures to replace declining production.

We may not be able to identify or complete the acquisition of properties with sufficient reserves or reservoirs to implement our business strategy. As we produce our existing reserves, we must identify, acquire and develop properties through new acquisitions or our level of production and cash flows will be adversely affected. The availability of properties for acquisition depends largely on the divesting practices of other oil and natural gas companies, commodity prices, general economic conditions and other factors that we cannot control or influence. A substantial decrease in the availability of proved oil and gas properties that meet our criteria in our areas of operation, or a substantial increase in the cost to acquire these properties, would adversely affect our ability to replace our reserves.

We may incur substantial impairment write-downs.

If management’s estimates of the recoverable reserves on a property are revised downward, if development costs exceed previous estimates or if oil and natural gas prices decline, we may be required to record additional noncash impairment write-downs in the future, which would result in a negative impact to our financial position. We review our proved oil and gas properties for impairment on a depletable unit basis when circumstances suggest there is a need for such a review. To determine if a depletable unit is impaired, we compare the carrying value of the depletable unit to the undiscounted future net cash flows by applying management’s estimates of future oil and gas prices to the estimated future production of oil and gas reserves over the economic life of the property. Future net cash flows are based upon our independent reservoir engineers’ estimates of proved reserves. In addition, other factors such as probable and possible reserves are taken into consideration when justified by economic conditions. For each property determined to be impaired, we recognize an impairment loss equal to the difference between the estimated fair value and the carrying value of the property on a depletable unit basis. Fair value is estimated to be the present value of the aforementioned expected future net cash flows. Any impairment charge incurred is recorded in accumulated depreciation, depletion, impairment and amortization to reduce our recorded basis in the asset. Each part of this calculation is subject to a large degree of judgment, including the determination of the depletable units’ estimated reserves, future cash flows and fair value. We recorded an impairment of $19.5 million for the year ended December 31, 2006 and no impairments in 2005 and 2004.

Management’s assumptions used in calculating oil and gas reserves or regarding the future cash flows or fair value of our properties are subject to change in the future. Any change could cause impairment expense to be recorded, impacting our net income or loss and our basis in the related asset. Any change in reserves directly impacts our estimate of future cash flows from the property, as well as the property’s fair value. Additionally, as management’s views related to future prices change, the change will affect the estimate of future net cash flows and the fair value estimates. Changes in either of these amounts will directly impact the calculation of impairment.

The oil and natural gas business involves many uncertainties and operating risks that can prevent us from realizing profits and can cause substantial losses.

Our development activities may be unsuccessful for many reasons, including cost overruns, equipment shortages and mechanical difficulties. Moreover, the successful drilling of a natural gas or oil well does not ensure a profit on investment. A variety of factors, both technical and market-related, can cause a well to become uneconomical or only marginally economic. In addition to their cost, unsuccessful wells can hurt our efforts to replace reserves.

The oil and natural gas business involves a variety of operating risks, including:

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fires;

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explosions;

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blow-outs and surface cratering;

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uncontrollable flows of natural gas, oil and formation water;

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pipe, cement, subsea well or pipeline failures;

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casing collapses;

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embedded oil field drilling and service tools;

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abnormally pressured formations;

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environmental accidents or hazards, such as natural gas leaks, oil spills, pipeline ruptures and discharges of toxic gases; and

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hurricanes and other natural disasters.

If we experience any of these problems, it could affect well bores, platforms, gathering systems and processing facilities, which could adversely affect our ability to conduct operations. We could also incur substantial losses in excess of our insurance coverage as a result of:

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injury or loss of life;

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severe damage to and destruction of property, natural resources and equipment;

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pollution and other environmental damage;

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clean-up responsibilities;

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regulatory investigation and penalties;

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suspension of our operations; and

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repairs to resume operations.

Offshore operations are also subject to a variety of operating risks peculiar to the marine environment, such as capsizing, collisions and damage or loss from hurricanes or other adverse weather conditions. These conditions can cause substantial damage to facilities and interrupt production. As a result, we could incur substantial liabilities that could reduce or eliminate the funds available for development or leasehold acquisitions, or result in loss of equipment and properties.

Terrorist attacks or similar hostilities may adversely impact our results of operations.

The terrorist attacks that took place in the United States on September 11, 2001 were unprecedented events that have created many economic and political uncertainties, some of which may materially adversely impact our business. Uncertainty surrounding military strikes or a sustained military campaign may affect our operations in unpredictable ways, including disruptions of fuel supplies and markets, particularly oil, and the possibility that infrastructure facilities, including pipelines, production facilities, processing plants and refineries, could be direct targets of, or indirect casualties of, an act of terror or war. The continuation of these developments may subject our operations to increased risks and, depending on their ultimate magnitude, could have a material adverse effect on our business, results of operations, financial condition and prospects.

Our insurance coverage may not be sufficient to cover some liabilities or losses that we may incur.

The occurrence of a significant accident or other event not fully covered by our insurance could have a material adverse effect on our operations and financial condition. Our insurance does not protect us against all operational risks. We do not carry business interruption insurance at levels that would provide enough funds for us to continue operating without access to other funds. For some risks, we may not obtain insurance if we believe the cost of available insurance is excessive relative to the risks presented. Because third party contractors and other service providers are used in our offshore operations, we may not realize the full benefit of workmen’s compensation laws in dealing with their employees. In addition, pollution and environmental risks generally are not fully insurable.

We may be unable to identify liabilities associated with the properties that we acquire or obtain protection from sellers against them.

The acquisition of properties requires us to assess a number of factors, including recoverable reserves, development and operating costs and potential environmental and other liabilities. Such assessments are inexact and inherently uncertain. In connection with the assessments, we perform a review of the subject properties, but such a review will not reveal all existing or potential problems. In the course of our due diligence, we may not inspect every well, platform or pipeline. We cannot necessarily observe structural and environmental problems, such as pipeline corrosion, when an inspection is made. We may not be able to obtain contractual indemnities from the seller for liabilities that it created. We may be required to assume the risk of the physical condition of the properties in addition to the risk that the properties may not perform in accordance with our expectations.

Competition in our industry is intense, and we are smaller and have a more limited operating history than some of our competitors in the Gulf of Mexico and in the North Sea.

We compete with major and independent oil and natural gas companies for property acquisitions. We also compete for the equipment and labor required to operate and to develop these properties. Some of our competitors have substantially greater financial and other resources than ATP. In addition, larger competitors may be able to absorb the burden of any changes in federal, state and local laws and regulations more easily than we can, which would adversely affect our competitive position. These competitors may be able to pay more for oil and natural gas properties and may be able to define, evaluate, bid for and acquire a greater number of properties than we can. Our ability to acquire additional properties and develop new and existing properties in the future will depend on our ability to conduct operations, to evaluate and select suitable properties and to consummate transactions in this highly competitive environment. In addition, some of our competitors have been operating in the Gulf of Mexico and in the North Sea for a much longer time than we have and have demonstrated the ability to operate through industry cycles.

We may suffer losses as a result of foreign currency fluctuations.

The net assets, net earnings and cash flows from our wholly owned subsidiaries in the U.K. and the Netherlands are based on the U.S. dollar equivalent of such amounts measured in the applicable functional currency. These foreign operations have the potential to impact our financial position due to fluctuations in the local currency arising from the process of re-measuring the local functional currency in the U.S. dollar. Any increase in the value of the U.S. dollar in relation to the value of the local currency will adversely affect our revenues from our foreign operations when translated into U.S. dollars. Similarly, any decrease in the value of the U.S. dollar in relation to the value of the local currency will increase our development costs in our foreign operations, to the extent such costs are payable in foreign currency, when translated into U.S. dollars. We have not utilized derivatives or other financial instruments to hedge the risk associated with the movement in foreign currencies.

Our success depends on our management team and other key personnel, the loss of any of whom could disrupt our business operations.

Our success will depend on our ability to retain and attract experienced geoscientists and other professional staff. As of December 31, 2006, we had 22 engineers, geologist/geophysicists and other technical personnel in our Houston office, two engineers, geologist/geophysicists and other technical personnel in our U.K. location and one engineer in our Netherlands office. We depend to a large extent on the efforts, technical expertise and continued employment of these personnel and members of our management team. If a significant number of them resign or become unable to continue in their present role and if they are not adequately replaced, our business operations could be adversely affected.

Members of our management team own a significant amount of common stock, giving them influence or control in corporate transactions and other matters, and the interests of these individuals could differ from those of other shareholders.

Members of our management team beneficially own approximately 27.06% of our outstanding shares of common stock as of November 13, 2007. As a result, these shareholders are in a position to significantly influence or control the outcome of matters requiring a shareholder vote, including the election of directors, the adoption of an amendment to our articles of incorporation or bylaws and the approval of mergers and other significant corporate transactions. Their control of ATP may delay or prevent a change of control of ATP and may adversely affect the voting and other rights of other shareholders. Two members of management, T. Paul Bulmahn and Gerald W. Schlief, have each previously entered into loan agreements with the same lender pursuant to which they pledged 1,250,000 and 118,500 shares of our common stock, respectively, to secure their loans. We have been advised by both officers that though each has repaid his loan in full, the lender has not yet returned to either his pledged shares. Both officers have commenced legal proceedings against the lender seeking the return of the pledged shares but the proceedings have not been resolved. In the event the 1,250,000 and 118,500 shares are not returned, our management team’s beneficial ownership would be reduced to 22.6% of our outstanding shares.

Rapid growth may place significant demands on our resources.

We have experienced rapid growth in our operations and expect that significant expansion of our operations will continue. Our rapid growth has placed, and our anticipated future growth will continue to place, a significant demand on our managerial, operational and financial resources due to:

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the need to manage relationships with various strategic partners and other third parties;

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difficulties in hiring and retaining skilled personnel necessary to support our business;

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the need to train and manage a growing employee base; and

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pressures for the continued development of our financial and information management systems.

If we have not made adequate allowances for the costs and risks associated with this expansion or if our systems, procedures or controls are not adequate to support our operations, our business could be adversely impacted.

We are subject to complex laws and regulations, including environmental regulations that can adversely affect the cost, manner or feasibility of doing business.

Development, production and sale of oil and natural gas in the Gulf of Mexico and in the North Sea are subject to extensive laws and regulations, including environmental laws and regulations. We may be required to make large expenditures to comply with environmental and other governmental regulations. Matters subject to regulation include:

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discharge permits for drilling operations;

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bonds for ownership, development and production of oil and gas properties;

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reports concerning operations; and

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taxation.

Under these laws and regulations, we could be liable for personal injuries, property damage, oil spills, discharge of hazardous materials, remediation and clean-up costs and other environmental damages. Failure to comply with these laws and regulations also may result in the suspension or termination of our operations and subject us to administrative, civil and criminal penalties. Moreover, these laws and regulations could change in ways that substantially increase our costs. Accordingly, any of these liabilities, penalties, suspensions, terminations or regulatory changes could materially adversely affect our financial condition and results of operations.

USE OF PROCEEDS

We intend to use the net proceeds we receive from the sale of securities by us as set forth in the applicable prospectus or prospectus supplement. Unless otherwise provided in the applicable prospectus supplement, we will not receive any proceeds from the sale of securities by any selling shareholder named in such prospectus supplement.

SELLING SHAREHOLDERS

To the extent that this prospectus is used by any selling shareholder to resell any of our securities, information with respect to the selling shareholder and the plan of distribution will be contained in a supplement to this prospectus.

THE SECURITIES WE OR THE SELLING SHAREHOLDERS MAY OFFER

The descriptions of the securities contained in this prospectus, together with any applicable prospectus or prospectus supplements, summarize all the material terms and provisions of the various types of securities that we or the selling shareholders may offer. We will describe in the applicable prospectus or prospectus supplement the particular terms of the securities offered by that prospectus or prospectus supplement. If we indicate in the applicable prospectus or prospectus supplement, the terms of the securities may differ from the terms we have summarized below. We will also include in the prospectus or prospectus supplement information, where applicable, about material United States federal income tax considerations relating to the securities, and the securities exchange, if any, on which the securities will be listed.

We may sell from time to time, in one or more offerings:

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common stock;

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preferred stock;

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depositary shares; and

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warrants to purchase any of the securities listed above.

In addition, our selling shareholders may from time to time sell common stock. In this prospectus, we refer to the common stock, preferred stock, depositary shares and warrants collectively as “securities”.

DESCRIPTION OF CAPITAL STOCK

Our authorized capital stock consists of 100,000,000 shares of common stock, par value $0.001 per share, and 10,000,000 shares of preferred stock, par value $0.001 per share. As of November 13, 2007, we have 30,632,351 outstanding shares of common stock, and no outstanding shares of preferred stock.

Common Stock

Subject to any special voting rights of any series of preferred stock that we may issue in the future, each share of common stock has one vote on all matters voted on by our shareholders, including the election of our directors. Because holders of common stock do not have cumulative voting rights, the holders of a majority of the shares of common stock can elect all of the members of the board of directors standing for election, subject to the rights, powers and preferences of any outstanding series of preferred stock.

No share of common stock affords any preemptive rights or is convertible, redeemable, assessable or entitled to the benefits of any sinking or repurchase fund. Holders of common stock will be entitled to dividends in the amounts and at the times declared by our board of directors in its discretion out of funds legally available for the payment of dividends.

Holders of common stock will share equally in our assets on liquidation after payment or provision for all liabilities and any preferential liquidation rights of any preferred stock then outstanding. All outstanding shares of common stock are fully paid and non-assessable.

Preferred Stock

At the direction of our board, we may issue shares of preferred stock from time to time. Our board of directors may, without any action by holders of the common stock:

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adopt resolutions to issue preferred stock in one or more classes or series;

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fix or change the number of shares constituting any class or series of preferred stock; and

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establish or change the rights of the holders of any class or series of preferred stock.

The rights of any class or series of preferred stock may include, among others:

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general or special voting rights;

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preferential liquidation or preemptive rights;

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preferential cumulative or noncumulative dividend rights;

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redemption or put rights; and

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conversion or exchange rights.

We may issue shares of, or rights to purchase, preferred stock the terms of which might:

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adversely affect voting or other rights evidenced by, or amounts otherwise payable with respect to, the common stock;

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discourage an unsolicited proposal to acquire us; or

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facilitate a particular business combination involving us.

Any of these actions could discourage a transaction that some or a majority of our shareholders might believe to be in their best interests or in which our shareholders might receive a premium for their stock over its then market price.

Rights Agreement

Our Board of Directors has adopted a Rights Agreement pursuant to which holders of our common stock will be entitled to purchase from us one one-hundredth of a share of our Junior Participating Preferred Stock if a third party acquires beneficial ownership of 15% or more of our common stock or if other specified events occur without our consent. In addition, the holders of our common stock will be entitled to purchase the stock of an Acquiring Person (as defined in the Rights Agreement) at a discount upon the occurrence of triggering events. The exercise price per right is $150, subject to adjustment. These provisions of the Rights Agreement could have certain anti-takeover effects because the rights provided to holders of our common stock under the Rights Agreement will cause substantial dilution to a person or group that acquires our common stock or engages in other specified events without the rights under the agreement having been redeemed or in the event of an exchange of the rights for common stock as permitted under the agreement.

Anti-Takeover Provisions of our Articles of Incorporation and Bylaws

The provisions of Texas law and our articles of incorporation and bylaws we summarize below may have an anti-takeover effect and may delay, defer or prevent a tender offer or takeover attempt that a shareholder might consider in his or her best interest, including those attempts that might result in a premium over the market price for the common stock.

Business Combinations Under Texas Law.We are a Texas corporation and, upon completion of the offering, will be subject to Part Thirteen of the Texas Business Corporation Act, known as the “Business Combination Law.” In general, this law will prevent us from engaging in a business combination with an affiliated shareholder, or any affiliate or associate of an affiliated shareholder, for a three-year period after the date such person became an affiliated shareholder, unless:

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our board of directors approves the acquisition of shares that causes such person to become an affiliated shareholder before the date such person becomes an affiliated shareholder,

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our board of directors approves the business combination before the date such person becomes an affiliated shareholder, or

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holders of at least two-thirds of our outstanding voting shares not beneficially owned by the affiliated shareholder or its affiliates or associates approve the business combination within six months after the date such person becomes an affiliated shareholder.

Under this law, any person that owns or has owned 20% or more of our voting shares during the preceding three-year period is an “affiliated shareholder.” The law defines “business combination” generally as including:

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mergers, share exchanges or conversions involving an affiliated shareholder,

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dispositions of assets involving an affiliated shareholder:

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having an aggregate value equal to 10% or more of the market value of our assets;

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having an aggregate value equal to 10% or more of the market value of our outstanding common stock; or

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representing 10% or more of our earning power or net income;

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issuances or transfers of securities by us to an affiliated shareholder other than on a pro rata basis;

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plans or agreements relating to our liquidation or dissolution involving an affiliated shareholder,

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reclassifications, recapitalizations, mergers or other transactions that would have the effect of increasing an affiliated shareholder’s percentage ownership of our outstanding voting stock, and

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the receipt of tax, guarantee, pledge, loan or other financial benefits by an affiliated shareholder other than proportionally as one of our shareholders.

Written Consent of Shareholders.Our articles of incorporation provide that any action by our shareholders must be taken at an annual or special meeting of shareholders. Special meetings of the shareholders may be called only by holders of not less than 50% of all the shares entitled to vote.

Advance Notice Procedure for Shareholder Proposals.Our bylaws establish an advance notice procedure for the nomination of candidates for election as directors as well as for shareholder proposals to be considered at annual meetings of shareholders. In general, notice of intent to nominate a director must contain specific information concerning the person to be nominated and must be delivered to or mailed and received at our principal executive offices as follows:

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With respect to an election to be held at the annual meeting of shareholders, not less than 90 days nor more than 120 days prior to the first anniversary date of the preceding year’s annual meeting of shareholders.

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With respect to an election to be held at a special meeting of shareholders for the election of directors, not earlier than the close of business on the 120th day prior to the special meeting and not later than the close of business on the later of the 90th day prior to the special meeting or the 10th day following the day on which public disclosure is first made of the date of the special meeting.

Notice of shareholders’ intent to raise business at an annual meeting must be delivered to or mailed and received at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary date of the preceding year’s annual meeting of shareholders. These procedures may operate to limit the ability of shareholders to bring business before a shareholders meeting, including with respect to the nomination of directors or considering any transaction that could result in a change of control.

Classified Board; Removal of Director.Our bylaws provide that the members of our board of directors are divided into three classes as nearly equal as possible. Each class is elected for a three-year term. At each annual meeting of shareholders,

approximately one-third of the members of the board of directors are elected for a three-year term and the other directors remain in office until their three-year terms expire. Furthermore, our bylaws provide that neither any director nor the board of directors may be removed without cause, and that any removal for cause would require the affirmative vote of the holders of at least a majority of the voting power of the outstanding capital stock entitled to vote for the election of directors. Thus, control of the board of directors cannot be changed in one year without removing the directors for cause as described above; rather, at least two annual meetings must be held before a majority of the members of the board of directors could be changed.

Limitation of Liability of Directors.Our articles of incorporation provide that no director shall be personally liable to ATP or its shareholders for monetary damages for breach of fiduciary duty as a director, except for liability as follows:

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for any breach of the director’s duty of loyalty to ATP or its shareholders;

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for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law;

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for an act or omission for which the liability of a director is expressly provided by an applicable statute; and

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for any transaction from which the director derived an improper personal benefit.

The effect of these provisions is to eliminate the rights of ATP and its shareholders, through derivative suits on behalf of ATP, to recover monetary damages against a director for a breach of fiduciary duty as a director, including breaches resulting from grossly negligent behavior, except in the situations described above.

Depositary Shares

General. We may, at our option, elect to issue fractional shares of preferred stock, rather than full shares of preferred stock. If such option is exercised, we may elect to have a depositary issue receipts for depositary shares, each receipt representing a fraction (to be set forth in any applicable prospectus or prospectus supplement relating to a particular series of preferred stock) of a share of a particular series of preferred stock as described below. The shares of any series of preferred stock represented by depositary shares will be deposited under a deposit agreement between us and a depositary. Subject to the terms of such a deposit agreement, each owner of a depositary share will be entitled, in proportion to the applicable fraction of a share of preferred stock represented by such depositary share, to all the rights and preferences of the preferred stock represented thereby (including dividend, voting, redemption and liquidation rights).

Any depositary shares will be evidenced by depositary receipts issued pursuant to such a deposit agreement. Depositary receipts will be distributed to those persons purchasing the fractional shares of preferred stock in accordance with the terms of an offering of the preferred stock. In connection with the issuance of any series of preferred stock represented by depositary shares, the forms of deposit agreement and depositary receipt will be filed as exhibits to this registration statement of which this prospectus is a part.

Pending the preparation of definitive engraved depositary receipts, a depositary may, upon our written order, issue temporary depositary receipts substantially identical to (and entitling the holders thereof to all the rights pertaining to) the definitive depositary receipts but not in definitive form. Definitive depositary receipts will be prepared thereafter without unreasonable delay, and temporary depositary receipts will be exchangeable for definitive depositary receipts at our expense.

Upon surrender of depositary receipts at the office of the depositary and upon payment of the charges provided in the deposit agreement and subject to the terms thereof, a holder of depositary receipts is entitled to have the depositary deliver to such holder the whole shares of preferred stock relating to the surrendered depositary receipts. Holders of depositary shares will be entitled to receive whole shares of the related series of preferred stock on the basis set forth in any applicable prospectus or prospectus supplement for such series of preferred stock, but holders of such whole shares will not thereafter be entitled to receive depositary shares therefor. If the depositary receipts delivered by the holder evidence a number of depositary shares in excess of the number of depositary shares representing the number of whole shares of the related series of preferred stock to be withdrawn, the depositary will deliver to such holder at the same time a new depositary receipt evidencing such excess number of depositary shares.

Dividends and Other Distributions.The depositary will distribute all cash dividends or other cash distributions received in respect of the preferred stock to the record holders of depositary shares relating to such preferred stock in proportion to the numbers of such depositary shares owned by such holders.

In the event of a distribution other than in cash, the depositary will distribute property received by it to the record holders of depositary shares entitled thereto, unless the depositary determines that it is not feasible to make such distribution, in which case the depositary may, with our approval, sell such property and distribute the net proceeds from such sale to such holders.

Redemption of Depositary Shares. If a series of preferred stock represented by depositary shares is subject to redemption, the depositary shares will be redeemed from the proceeds received by the depositary resulting from the redemption, in whole or in part, of such series of preferred stock held by the depositary. The redemption price per depositary share will be equal to the applicable fraction of the redemption price per share payable with respect to such series of the preferred stock. Whenever we redeem shares of preferred stock held by the depositary, the depositary will redeem as of the same redemption date the number of depositary shares representing shares of preferred stock so redeemed. If less than all the depositary shares are to be redeemed, the depositary shares to be redeemed will be selected by lot or ratably as may be determined by the depositary.

Voting the Preferred Shares. Upon receipt of notice of any meeting at which the holders of the preferred stock are entitled to vote, the depositary will mail the information contained in such notice of meeting to the record holders of the depositary shares relating to such preferred stock. Each record holder of such depositary shares on the record date (which will be the same date as the record date for the preferred stock) will be entitled to instruct the depositary as to the exercise of the voting rights pertaining to the amount of the preferred stock represented by such holder’s depositary shares. The depositary will endeavor, insofar as practicable, to vote the amount of the preferred stock represented by such depositary shares in accordance with such instructions, and we will agree to take all action which may be deemed necessary by the depositary in order to enable the depositary to do so. The depositary will abstain from voting shares of the preferred stock to the extent it does not receive specific instructions from the holders of depositary shares representing such preferred stock.

Amendment and Termination of the Deposit Agreement. The form of depositary receipt evidencing the depositary shares and any provision of any deposit agreement may at any time be amended by agreement between us and the depositary. However, any amendment which materially and adversely alters the rights of the holders of depositary shares will not be effective unless such amendment has been approved by the holders of at least a majority of the depositary shares then outstanding. The deposit agreement may be terminated by us or the depositary only if (1) all outstanding depositary shares have been redeemed or (2) there has been a final distribution in respect to the preferred stock in connection with our liquidation, dissolution or winding up and such distribution has been distributed to the holders of depositary receipts.

Charges of Depositary. We will pay all transfer and other taxes and governmental charges arising solely from the existence of the depositary arrangements. We will pay charges of the depositary in connection with the initial deposit of the preferred stock and any redemption of the preferred stock. Holders of depositary receipts will pay other transfer and other taxes and governmental charges and such other charges as are expressly provided in the deposit agreement to be for their accounts.

Miscellaneous. The depositary will forward to the record holders of the depositary shares relating to such preferred stock all reports and communications from us which are delivered to the depositary.

Neither the depositary nor we will be liable if it is prevented or delayed by law or any circumstance beyond its control in performing its obligations under any deposit agreement. The obligations of us and the depositary under the deposit agreement will be limited to performance in good faith of their duties thereunder, and they will not be obligated to prosecute or defend any legal proceeding in respect of any depositary shares or preferred stock unless satisfactory indemnity is furnished. They may rely upon written advice of counsel or accountants, or information provided by persons presenting preferred stock for deposit, holders of depositary receipts or other persons believed to be competent and on documents believed to be genuine.

Resignation and Removal of Depositary. The depositary may resign at any time by delivering to us notice of its election to do so, and we may at any time remove the depositary, any such resignation or removal to take effect upon the appointment of a successor depositary and its acceptance of such appointment. Such successor depositary must be appointed within 60 days after delivery of the notice of resignation or removal and must be a bank or trust company having its principal office in the United States and having a combined capital and surplus of at least $50,000,000.

Transfer Agent

The transfer agent for our common stock is American Stock Transfer & Trust Company.

DESCRIPTION OF WARRANTS

The following description, together with the additional information we may include in any applicable prospectus or prospectus supplement, summarizes the material terms and provisions of the warrants that we may offer under this prospectus and the related warrant agreements and warrant certificates. While the terms summarized below will apply generally to any warrants that we may offer, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus or prospectus supplement. If we indicate in the prospectus or prospectus supplement, the terms of any warrants offered under that prospectus or prospectus supplement may differ from the terms described below. Specific warrant agreements will contain additional important terms and provisions and will be incorporated by reference as an exhibit to the registration statement that includes this prospectus.

General

We may issue warrants for the purchase of common stock or preferred stock in one or more series. We may issue warrants independently or together with common stock and preferred stock, and the warrants may be attached to or separate from these securities.

We will evidence each series of warrants by warrant certificates that we will issue under a separate agreement. We may enter into the warrant agreement with a warrant agent. We will indicate the name and address and other information regarding the warrant agent in the applicable prospectus or prospectus supplement relating to a particular series of warrants.

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including in the case of warrants to purchase common stock or preferred stock, the right to receive dividends, if any, or, payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.

Additional Information

We will describe in an applicable prospectus or prospectus supplement the terms of the series of warrants, including:

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the offering price and aggregate number of warrants offered;

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the currency for which the warrants may be purchased;

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if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

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if applicable, the date on and after which the warrants and the related securities will be separately transferable;

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in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

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the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreement and the warrants;

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the terms of any rights to redeem or call the warrants;

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any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;

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the dates on which the right to exercise the warrants will commence and expire;

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the manner in which the warrant agreement and warrants may be modified;

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a discussion on any material or special United States federal income tax consequences of holding or exercising the warrants;

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the terms of the securities issuable upon exercise of the warrants; and

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any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

Exercise of Warrants

Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus or prospectus supplement at the exercise price that we describe in the applicable prospectus or prospectus supplement. Unless we otherwise specify in the applicable prospectus or prospectus supplement, holders of the warrants may exercise the warrants at any time up to 5 p.m., Eastern time, on the expiration date that we set forth in the applicable prospectus or prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

Holders of the warrants may exercise the warrants by delivering the warrant certificate representing the warrants to be exercised together with specified information, and paying the required amount to the warrant agent in immediately available funds, as provided in the applicable prospectus or prospectus supplement. We will set forth on the reverse side of the warrant certificate and in the applicable prospectus or prospectus supplement the information that the holder of the warrant will be required to deliver to the warrant agent.

Upon receipt of the required payment and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus or prospectus supplement, we will issue and deliver the securities purchasable upon such exercise. If fewer than all of the warrants represented by the warrant certificate are exercised, then we will issue a new warrant certificate for the remaining amount of warrants. If we so indicate

in the applicable prospectus or prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

Enforceability of Rights by Holders of Warrants

Each warrant agent will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

LEGAL OWNERSHIP OF SECURITIES

We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in “street name”. Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or if we issue the securities only in global form.

For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of the indenture or for other purposes. In such an event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the holders contact the indirect holders is up to the holders.

Special Considerations for Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

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how it handles securities payments and notices;

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whether it imposes fees or charges;

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how it would handle a request for the holders’ consent, if ever required;

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whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;

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how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and

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if the securities are in book-entry form, how the depositary’s rules and procedures will affect these matters.

Global Securities

A global security is a security held by a depositary that represents one or any other number of individual securities. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, The Depository Trust Company, New York, New York, known as DTC, will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under “Special Situations When a Global Security will be Terminated”. As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus or prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations for Global Securities

As an indirect holder, an investor’s rights relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only in the form of a global security, an investor should be aware of the following:

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an investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;

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an investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe under “Legal Ownership of Securities”;

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an investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;

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an investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

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the depositary’s policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor’s interest in a global security. We and any applicable trustee have no responsibility for any aspect of the depositary’s actions or for its records of ownership interests in a global security. We and the trustee also do not supervise the depositary in any way;

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the depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

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financial institutions that participate in the depositary’s book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities. There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security will be Terminated

In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

The global security will terminate when the following special situations occur:

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if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;

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if we notify any applicable trustee that we wish to terminate that global security; or

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if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

The prospectus or prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the prospectus or prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

PLAN OF DISTRIBUTION

We or our selling shareholders may sell the securities through underwriters or dealers, through agents, or directly to one or more purchasers. The accompanying prospectus or prospectus supplement will describe the terms of the offering of the securities, including:

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the name or names of any underwriters or any selling shareholders;

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the purchase price of shares of common stock being offered and the proceeds we or the selling shareholders will receive from the sale;

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any over-allotment options pursuant to which underwriters may purchase additional shares of common stock from us or the selling shareholders;

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any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation; and

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any discounts or concessions allowed or reallowed or paid to dealers.

If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of the sale. The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We or the selling shareholders may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all the securities offered by the prospectus or prospectus supplement. We or the selling shareholders may change from time to time the public offering price and any discounts or concessions allowed or reallowed or paid to dealers. We or the selling shareholders may use underwriters with whom we or they have a material relationship.

We will describe such relationships in the prospectus supplement naming the underwriter and the nature of any such relationship.

We or the selling shareholders may sell securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of the securities, and we or the selling shareholders will describe any commissions we will pay the agent in the prospectus supplement. Unless the prospectus or prospectus supplement states otherwise, the agent will act on a best efforts basis for the period of its appointment.

We or the selling shareholders may provide agents and underwriters with indemnification against civil liabilities related to this offering, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities. Agents and underwriters may engage in transactions with, or perform services for, us or the selling shareholders in the ordinary course of business.

Rules of the Securities and Exchange Commission may limit the ability of any underwriters to bid for or purchase securities before the distribution of the securities is completed. However, underwriters may engage in the following activities in accordance with the rules:

Stabilizing transactions.Underwriters may make bids or purchases for the purpose of pegging, fixing or maintaining the price of the shares, so long as stabilizing bids do not exceed a specified maximum.

Over-allotments and syndicate covering transactions.Underwriters may sell more shares of our common stock than the number of shares that they have committed to purchase in any underwritten offering. This over-allotment creates a short position for the underwriters. This short position may involve either “covered” short sales or “naked” short sales. Covered short sales are short sales made in an amount not greater than the underwriters’ over-allotment option to purchase additional shares in any underwritten offering. The underwriters may close out any covered short position either by exercising their over-allotment option or by purchasing shares in the open market. To determine how they will close the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market, as compared to the price at which they may purchase shares through the over-allotment option. Naked short sales are short sales in excess of the over-allotment option. The underwriters must close out any naked position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that, in the open market after pricing, there may be downward pressure on the price of the shares that could adversely affect investors who purchase shares in the offering.

Penalty bids.If underwriters purchase shares in the open market in a stabilizing transaction or syndicate covering transaction, they may reclaim a selling concession from other underwriters and selling group members who sold those shares as part of the offering.

Similar to other purchase transactions, an underwriter’s purchases to cover the syndicate short sales or to stabilize the market price of our securities may have the effect of raising or maintaining the market price of our securities or preventing or mitigating a decline in the market price of our securities. As a result, the price of the securities may be higher than the price that might otherwise exist in the open market. The imposition of a penalty bid might also have an effect on the price of shares if it discourages resales of the securities.

If commenced, the underwriters may discontinue any of the activities at any time.

Any underwriters who are qualified market makers on The NASDAQ Global Select Market may engage in passive market making transactions in the securities on The NASDAQ Global Select Market in accordance with Rule 103 of Regulation M, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the securities. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded.

In compliance with guidelines of the Financial Industry Regulatory Authority, or FINRA, the maximum consideration or discount to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amount of the securities offered pursuant to this prospectus and any applicable prospectus supplement.

LEGAL MATTERS

The validity of the securities offered hereby has been passed upon for us by Jackson Walker L.L.P., Houston, Texas. In connection with particular offerings of securities in the future, and if stated in the applicable prospectus supplement, the

validity of the securities will be passed on for any underwriters or agents by such counsel named in the prospectus supplement.

EXPERTS

The consolidated financial statements, the related financial statement schedule, and management’s report on the effectiveness of internal control over financial reporting incorporated in this prospectus by reference from our Annual Report on Form 10-K for the year ended December 31, 2006 have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their report, which is incorporated herein by reference (which report (1) expressed an unqualified opinion on the consolidated financial statements and financial statement schedule and includes an explanatory paragraph referring to our adoption of Statement of Financial Accounting Standards No. 123(R), “Share-Based Payment”, (2) expressed an unqualified opinion on management’s assessment regarding the effectiveness of internal control over financial reporting, and (3) expressed an unqualified opinion on the effectiveness of internal control over financial reporting), and has been so incorporated in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

Atp Oil & Gas (ATPGQ) Inactive 424B5Prospectus supplement for primary offering

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