Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yesþ     Noo

     Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a non-accelerated filer.smaller reporting company. See definition of “accelerated filer,” “large accelerated filer” and large accelerated filer”“smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated fileroþ                      Accelerated filerþo                      Non-accelerated filero                      Smaller reporting companyo

     Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yeso      Noþ

     The registrant had 32,360,53852,774,728 common units and 7,000,000 subordinated units outstanding as of October 31, 2007.April 30, 2008.

     Certain matters contained in this report include “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements discuss our expected future results based on current and pending business operations.

     All statements, other than statements of historical facts, included in this report which address activities, events or developments that we expect, believe or anticipate will exist or may occur in the future, are forward-looking statements. Forward-looking statements can be identified by various forms of words such as “anticipates,” “believes,” “could,” “may,” “should,” “continues,” “estimates,” “expects,” “forecasts,” “might,” “planned,” “potential,” “projects,” “scheduled” or similar expressions. These forward-looking statements include, among others, statements regarding:

     Forward-looking statements are based on numerous assumptions, uncertainties and risks that could cause future events or results to be materially different from those stated or implied in this document. Many of the factors that will determine these results are

     Given the uncertainties and risk factors that could cause our actual results to differ materially from those contained in any forward-looking statement, we caution investors not to unduly rely on our forward-looking statements. We disclaim any obligations to and do not intend to update the above list or to announce publicly the result of any revisions to any of the forward-looking statements to reflect future events or developments.

     Because forward-looking statements involve risks and uncertainties, we caution that there are important factors, in addition to those listed above, that may cause actual results to differ materially from those contained in the forward-looking statements. For a detailed discussion of those factors, see Part I, Item IA1A “Risk Factors” in our annual report on Form 10-K for the year ended December 31, 2006.2007, and Part II, Item 1A. Risk Factors of this quarterly report on Form 10-Q.

     Unless the context clearly indicates otherwise, references in this report to “we,” “our,” “us” or like terms refer to Williams Partners L.P. and its subsidiariessubsidiaries. Unless the context clearly indicates otherwise, references to “we,” “our,” and “us” include the operations of Wamsutter LLC (Wamsutter) and Discovery Producer Services LLC (“Discovery”)(Discovery) in which we own a 60% interest.interests accounted for as equity investments that are not consolidated in our financial statements. When we refer to Wamsutter or Discovery by name, we are referring exclusively to itstheir businesses and operations.

     We are a Delaware limited partnership that was formedprincipally engaged in February 2005 to acquirethe business of gathering, transporting, processing and owntreating natural gas and fractionating and storing natural gas liquids (NGL). Operations of our businesses are located in the United States and are organized into three reporting segments: (1) a 40% interestGathering and Processing — West, (2) Gathering and Processing — Gulf and (3) NGL Services. Our Gathering and Processing — West segment includes the Four Corners gathering and processing operations and our equity investment in Discovery; (2)Wamsutter. Our Gathering and Processing — Gulf segment includes the Carbonate Trend gathering pipeline offand our equity investment in Discovery. Our NGL Services segment includes the coast of Alabama; (3) three integrated natural gas liquids (“NGL”) productConway fractionation and storage facilities near Conway, Kansas; and (4) a 50% undivided ownership interest in a fractionator near Conway, Kansas. Our initial public offering (the “IPO”) closed in August 2005. Williams Partners GP LLC, a Delaware limited liability company, was also formed in February 2005 to serve as our general partner. In addition, we formed Williams Partners Operating LLC (“OLLC”), an operating limited liability company (wholly owned by us), through which all our activities are conducted.

     On June 28, 2007, we closed on the acquisition of an additional 20% interest in Discovery from Williams Energy, L.L.C. and WES for aggregate considerationWilliams Energy Services, LLC, bringing our total ownership of $78.0 million in cash.Discovery to 60%. This transaction was effective July 1, 2007. Because this additional 20% interest in Discovery was purchased from an affiliate of The Williams Companies, Inc. (Williams), the transaction was between entities under common control, and has been accounted for at historical cost. Accordingly our consolidated financial statements and notes reflect the combined historical results of our investment in Discovery throughout the periods presented. The effect of recasting our financial statements to account for this common control exchange increased net income $1.3 million for the first quarter of 2007. The acquisition had no impact on earnings per unit as pre-acquisition earnings were allocated to the general partner.

     On December 11, 2007, we acquired certain ownership interests in Wamsutter, consisting of 100% of the Class A limited liability company interests and 20 Class C units representing 50% of the initial Class C ownership interests (collectively the Wamsutter Ownership Interests) Because the Wamsutter Ownership Interests were purchased from an affiliate of Williams, the transaction was between entities under common control, and has been accounted for at historical cost. Accordingly, our consolidated financial statements and notes have been restated to reflect the combined historical results of our investment in DiscoveryWamsutter throughout the periods presented. We now own 60%The effect of Discovery. We continuerecasting our financial statements to account for this investment under the equity method due to the voting provisions of Discovery’s limited liability company agreement which provide the other member of Discovery significant participatory rights such that we do notcommon control the investment. The acquisitionexchange increased net income $11.3 million for the nine months ended September 30, 2007 and 2006 by $2.6 million and $5.1 million, respectively. Thefirst quarter of 2007. This acquisition had nodoes not impact on earnings per unit for periods prior to the acquisition as pre-acquisition earnings were allocated to theour general partner.

     The accompanying interim consolidated financial statements do not include all the notes in our annual financial statements and, therefore, should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Form 8-K,10-K, filed August 29, 2007,February 26, 2008, for the year ended December 31, 2006.2007. The accompanying consolidated financial statements include all normal recurring adjustments that, in the opinion of management, are necessary to present fairly our financial position at September 30, 2007,March 31, 2008, and results of operations for the three and nine months ended September 30,March 31, 2008 and 2007 and 2006 and cash flows for the ninethree months ended September 30, 2007March 31, 2008 and 2006.2007. All intercompany transactions have been eliminated. Certain amounts have been reclassified to conform to the current classifications.

     The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in our Consolidated Financial Statementsthe consolidated financial statements and accompanying notes. Actual results could differ from those estimates.

enhanced quantitative, qualitative and credit risk disclosures. The Statement requires quantitative disclosure in a tabular format about the fair value on specified election dates. Unrealizedvalues of derivative instruments in the statement of financial position, gains and losses on derivative instruments in the statement of financial performance and information about where these items for which the fair value option has been elected will beare reported in earnings. The fair value option may be applied onthe financial statements. Also required in the tabular presentation is a separation of hedging and non-hedging activities. Qualitative disclosures include outlining objectives and strategies for using derivative instruments in terms of underlying risk exposures, use of derivatives for risk management and other purposes and accounting designation, and an instrument-by-instrument basis with a few exceptions, is irrevocableunderstanding of the volume and is applied only to entire instruments and not to portionspurpose of instruments.derivative activity. Credit risk disclosures provide information about credit risk related contingent features included in derivative agreements. SFAS No. 159161 also amends SFAS No. 107, “Disclosures about Fair Value of Financial Instruments,” to clarify that disclosures about concentrations of credit risk should include derivative instruments. This Statement is effective asfor financial statements issued for fiscal years and interim periods beginning after November 15, 2008, with early application encouraged. We plan to apply this Statement beginning in 2009. This Statement encourages, but does not require, comparative disclosures for earlier periods at initial adoption. We will assess the application of this Statement on our disclosures in our consolidated financial statements.

     In March 2008, the FASB ratified the decisions reached by the Emerging Issues Task Force (EITF) with respect to EITF Issue No. 07-4, “Application of the beginningTwo-Class Method under FASB Statement No. 128,Earnings per Share,to Master Limited Partnerships.” EITF Issue No. 07-4 states, among other things, that the calculation of earnings per unit should not reflect an allocation of undistributed earnings to the incentive distribution right (IDR) holders beyond amounts distributable to IDR holders under the terms of the partnership agreement. As described in Note 3, under current generally accepted accounting principles, we calculate earnings per unit as if all the earnings for the period had been distributed, which results in an additional allocation of income to the general partner (the IDR holder) in quarterly periods where an assumed incentive distribution, calculated as if all earnings for the period had been distributed, exceeds the actual incentive distribution. Following the adoption of the guidance in EITF Issue No. 07-4, we will no longer calculate assumed incentive distributions. The final consensus is effective beginning with the first interim period of the fiscal year beginning after NovemberDecember 15, 20072008, and should notmust be retrospectively applied retrospectively to fiscal years beginning priorall periods presented. Early application is prohibited. Retrospective application of this guidance will result in a decrease in the income allocated to the effective date, except as permitted for early adoption. We will adopt SFAS No. 159 on January 1, 2008. Ongeneral partner and an increase in the adoption date, an entity may elect the fair value option for eligible items existing at that date and the adjustmentincome allocated to limited partners for the initial remeasurementamount that any assumed incentive distribution exceeded the actual incentive distribution paid during that period. Certain of those items to fair value shouldour historical periods’ earnings per unit will be reportedrevised as a cumulative effect adjustment toresult of this change. Adoption of this new standard only impacts the opening balanceallocation of retained earnings. We continue to assess whether to apply the provisionsearnings for purposes of SFAS No. 159 to eligible financial instruments in place on the adoption datecalculating our earnings per limited partner unit and the relatedwill have no impact on our Consolidated Financial Statements.results of operations or distributions of available cash to unitholders and our general partner.

     The allocation of net income between our general partner and limited partners, as reflected in the Consolidated Statement of Partners’ Capital, for the three months and nine months ended September 30, 2007 and 2006 is as follows (in thousands):

     OutOur right of period adjustmentsway agreement with the Jicarilla Apache Nation (JAN), which covered certain gathering system assets in Rio Arriba County of northern New Mexico, expired on December 31, 2006. We currently operate our gathering assets on the JAN lands pursuant to correcta special business license granted by the JAN which expires on August 31, 2008, and are negotiating with the JAN to sell them these gathering assets. The special business license requires the execution of a purchase and sale agreement for these gathering assets on or before May 31. It is anticipated that this sale will be completed during the third or fourth quarter of 2008. As a result of the maturation of negotiations during the first quarter of 2008, these assets have been classified as held for sale on the consolidated balance sheet and include property, plant and equipment. Our management believes the expected proceeds from the sale of these assets will substantially exceed their carrying value of our$11.3 million. The gathering system assets being sold are part of the Gathering and liabilities reflected in Revenues or Costs and expenses in our Consolidated Statements of Income are summarized in the following table (in thousands):

     The summarized financial position and results of operations for 100% of Discovery are presented below (in thousands):

     Long-term debt at March 31, 2008 and Long-Term DebtDecember 31, 2007 is as follows:

     Credit Facilities

     We may borrow up to $75.0have a $450.0 million under Williams’ $1.5 billionsenior unsecured credit agreement with Citibank, N.A. as administrative agent, comprised initially of a $200.0 million revolving credit facility which is available for borrowings and letters of credit. Pursuant to an amendment dated May 9, 2007, borrowings undercredit and a $250.0 million term loan. Under certain conditions, the Williams facility mature in May 2012. Our $75.0 million borrowing limit under Williams’ revolving credit facility is available for general partnership purposes, including acquisitions, but onlymay be increased up to the extent that sufficient amounts remain unborrowed by Williams and its other subsidiaries. At September 30, 2007, letters of credit totaling $28.0 million had been issued on behalf of Williams, none on behalf of the Partnership, by the participating institutionsan additional $100.0 million. Borrowings under this facilityagreement must be repaid by December 11, 2012. At March 31, 2008, we had a $250.0 million term loan outstanding under the term loan provisions and no amounts outstanding under the revolving credit loans were outstanding.facility.

     We also have a $20.0 million revolving credit facility with Williams as the lender. The facility is available exclusively to fund working capital borrowings. Borrowings under the credit facility will mature on June 29,20, 2009. We are required to reduce all borrowings under this facility to zero for a period of at least 15 consecutive days once each 12-month period prior to the maturity date of the facility. As of September 30, 2007,March 31, 2008, we havehad no outstanding borrowings under the working capital credit facility.

     In connection withOn January 9, 2008, we sold an additional 800,000 common units to the issuancesunderwriters upon the underwriters’ partial exercise of their option to purchase additional common units pursuant to our common unit offering in December 2007 used to finance our acquisition of the Wamsutter Ownership Interests. We used the net proceeds from the partial exercise of the underwriters’ option to redeem 800,000 common units from an affiliate of Williams at a price per common unit of $36.24 ($37.75, net of underwriter discount).

     On January 28, 2008, our general partner’s board of directors confirmed that the financial test contained in our partnership agreement required for conversion of all of our $600.0 millionoutstanding subordinated units into common units had been satisfied. Accordingly, our 7,000,000 subordinated units held by four subsidiaries of 7.25% senior unsecured notesWilliams converted into common units on December 13, 2006 and $150.0 million of 7.5% senior unsecured notesa one-for-one basis on June 20, 2006, sold in private debt placements to qualified institutional buyers in accordance with Rule 144A under the Securities Act and outside the United States in accordance with Regulations under the Securities Act, we entered into registration rights agreements with the initial purchasers of the senior unsecured notes. Under these agreements, we agreed to conduct a registered exchange offer of exchange notes in exchange for the senior unsecured notes or cause to become effective a shelf registration statement providing for resale of the senior unsecured notes. We launched exchange offers for both series on April 10, 2007 and they were successfully closed on May 11, 2007.February 19, 2008.

     Accounting policy

nonfinancial assets and nonfinancial liabilities that are not recognized or disclosed on a recurring basis. SFAS No. 157 requires two distinct transition approaches; (i) cumulative-effect adjustment to beginning retained earnings for whichcertain financial instrument transactions and (ii) prospectively as of the normal purchasesdate of adoption through earnings or other comprehensive income, as applicable for all other instruments. Upon adopting SFAS No. 157, we applied a prospective transition as we did not have financial instrument transactions that required a cumulative-effect adjustment to beginning retained earnings.

     Fair value is the price that would be received to sell an asset or the amount paid to transfer a liability in an orderly transaction between market participants (an exit price) at the measurement date. Fair value is a market based measurement considered from the perspective of a market participant. We use market data or assumptions that market participants would use in pricing the asset or liability, including assumptions about risk and normal sales exception has been elected, on the Consolidated Balance Sheetrisks inherent in other current assets, other accrued liabilities, otherthe inputs to the valuation. These inputs can be readily observable, market corroborated, or unobservable. We primarily apply a market approach for recurring fair value measurements using the best available information while utilizing valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs where possible.

     SFAS No. 157 establishes a fair value hierarchy that prioritizes the inputs used to measure fair value. The hierarchy gives the highest priority to quoted prices in active markets for identical assets or other noncurrent liabilities.liabilities (Level 1 measurement) and the lowest priority to unobservable inputs (Level 3 measurement). We determine the current and noncurrent classificationclassify fair value balances based on the timingobservability of expected future cash flowsthose inputs. The three levels of individualthe fair value hierarchy are as follows:

     At March 31, 2008 all of our derivative assets and liabilities which are valued at fair value are included in Level 3 and include $1.5 million of energy commodity derivative assets and $1.5 million of energy commodity derivative liabilities. These derivatives include commodity based financial swap contracts.

     The accounting fordetermination of fair value also incorporates factors such as including the credit standing of the counterparties involved, our nonperformance risk on our liabilities, the impact of credit enhancements (such as cash deposits and letters of credit) and the time value of money.

     The following table sets forth a reconciliation of changes in the fair value of net derivatives is governed by SFAS No. 133, “Accounting for Derivative Instruments and Hedging Activities,” and depends on whether the derivative has been designated in a hedging relationship and what type of hedging relationship it is. For a derivative to qualify for designation in a hedging relationship, it must meet specific criteria and we must maintain appropriate documentation. We establish hedging relationships pursuant to our risk management policies. We evaluate the hedging relationships at the inception of the hedge and on an ongoing basis to determine whether the hedging relationship is, and is expected to remain, highly effective in achieving offsetting changes in fair value or cash flows attributable to the underlying risk being hedged. We also regularly assess whether the hedged forecasted transaction is probable of occurring. If a derivative ceases to be or is no longer expected to be highly effective, or if we believe the likelihood of occurrence of the hedged forecasted transaction is no longer probable, hedge accounting is discontinued prospectively, and future changesclassified as Level 3 in the fair value ofhierarchy for the derivative are recognized currently in other revenues.period January 1, 2008 through March��31, 2008.

     Realized and unrealized gains (losses) included in net income for the effective portion of the change in fair value of the derivative isabove period are reported in other comprehensive loss and reclassified into earningsrevenues in the period in which the hedged item affects earnings. Any ineffective portionour Consolidated Statement of the derivative’s change in fair value is recognized currently in other revenues. Gains or losses deferred in accumulated other comprehensive loss associated with terminated derivatives, derivatives that cease to be highly effective hedges, derivatives for which the forecasted transaction is reasonably possible but no longer probable of occurring, and cash flow hedges that have been otherwise discontinued remain in accumulated other comprehensive loss until the hedged item affects earnings. If it becomes probable that the forecasted transaction designated as the hedged item in a cash flow hedge will not occur, any gain or loss deferred in accumulated other comprehensive loss is recognized in other revenues at that time. The change in likelihood of a forecasted transaction is a judgmental decision that includes qualitative assessments made by management.Income.

     Environmental Matters-Four Corners.Current New Mexicofederal regulations require that certain unlined liquid containment pits located near named rivers and catchment areas be taken out of use, and current state regulations requiredrequire all unlined, earthen pits to be either permitted or closed by December 31, 2005. Operating under a New Mexico Oil Conservation Division-approved work plan, we have physically closed all of our pits identifiedthat were slated for administrative closure under those regulations, and administrative closureregulations. We are presently awaiting agency approval is pendingof the closures for 40 to 50 of those pits.

     We are also a participant in certain hydrocarbon removal and groundwater monitoring activities associated with certain well sites in New Mexico. Of nine remaining active sites, product removal is ongoing at seven and groundwater monitoring is ongoing at each site. As groundwater concentrations reach and sustain closure criteria levels and state regulator approval is received, the sites will be properly abandoned. We expect the remaining sites will be closed within four to eight years.

     In April 2007, the New Mexico Environment Department’s Air Quality Bureau (NMED) issued a Notice of Violation (NOV) to Four Corners that alleges various emission and reporting violations in connection with our Lybrook gas processing plant’s flare and leak detection and repair program. The NMED proposed a penalty of approximately $3 million. We are discussing the basis for and the scope of the proposed penalty with the NMED.

We have accrued liabilities totaling $0.7$1.5 million at September 30, 2007March 31, 2008 for these environmental activities. It is reasonably possible that we will incur losses in excess of our accrual for these matters. However, a reasonable estimate of such amounts cannot be determined at this time because actual costs incurred will depend on the actual number of contaminated sites identified, the amount and extent of contamination discovered, the final cleanup standards mandated by governmental authorities, negotiations with the applicable agencies, and other factors.

     We are subject to extensive federal, state and local environmental laws and regulations which affect our operations related to the construction and operation of our facilities. Appropriate governmental authorities may enforce these laws and regulations with a variety of civil and criminal enforcement measures, including monetary penalties, assessment and remediation requirements and injunctions as to future compliance. We have not been notified and are not currently aware of any material noncompliance under the various applicable environmental laws and regulations.

     Environmental Matters-Conway.We are a participant in certain environmental remediation activities associated with soil and groundwater contamination at our Conway storage facilities. These activities relate to four projects that are in various remediation stages including assessment studies, cleanups and/or remedial operations and monitoring. We continue to coordinate with the Kansas Department of Health and Environment (“KDHE”)(KDHE) to develop screening, sampling, cleanup and monitoring programs. The costs of such activities will depend upon the program scope ultimately agreed to by the KDHE and are expected to be paid over the next two to nine years.

     In 2004, we purchased an insurance policy that covers up to $5.0 million of remediation costs until an active remediation system is in place or April 30, 2008, whichever is earlier, excluding operation and maintenance costs and ongoing monitoring costs for these projects to the extent such costs exceed a $4.2 million deductible, of which $2.7$3.1 million has been incurred to date from the onset of the policy. The policy also covers costs incurred as a result of third party claims associated with then existing but unknown contamination related to the storage facilities. The aggregate limit under the policy for all claims is $25.0 million. We do not expect to submit any claims under this insurance policy prior to its expected expiration date on April 30, 2008. In addition, under an omnibus agreement with Williams entered into at the closing of our IPO, Williams agreed to indemnify us for the $4.2 million deductible not covered by the insurance policy, excluding costs of project management and soil and groundwater monitoring. There is a $14.0 million cap on the total amount of indemnity coverage under the omnibus agreement, which will be reduced by actual recoveries under the environmental insurance policy.agreement. There is also a three-year time limitation from the August 23, 2005 IPO closing date. The benefit of this indemnification is accounted for as a capital contribution to us by Williams as the costs are reimbursed. We estimate that the approximate cost of this project management and soil and groundwater monitoring associated with the four remediation projects at the Conway storage facilities and for which we will not be indemnified will be approximately $0.2 million to $0.4 million per year following the completion of the remediation work. At September 30, 2007,March 31, 2008, we had accrued liabilities totaling $4.3$3.2 million for these costs. It is reasonably possible that we will incur losses in excess of our accrual for these matters. However, a reasonable estimate of such amounts cannot be determined at this time because actual costs incurred will depend on the actual number of contaminated sites identified, the amount and extent of contamination discovered, the final cleanup standards mandated by KDHE and other governmental authorities and other factors.

     Will Price.In 2001, certainwe were named, along with other subsidiaries of Williams, including those that owned Four Corners, were named as defendants in a nationwide class action lawsuit in Kansas state court that had been pending against other defendants, generally pipeline and gathering companies, since 2000. The plaintiffs alleged that the defendants have engaged in mismeasurement techniques that distort the heating content of natural gas, resulting in an alleged underpayment of royalties to the class of producer plaintiffs and sought an unspecified amount of damages. We cannot reasonably estimate or quantify any potential liability. The defendants have opposed class certification and a hearing on the plaintiffs’ second motion to certify the class was held on April 1, 2005. We are awaiting a decision from the court. The amount of any possible liability cannot be reasonably estimated at this time.

     Grynberg.In 1998, the Department of Justice informed Williams that Jack Grynberg, an individual, had filed claims on behalf of himself and the federal government, in the United States District Court for the District of Colorado under the False Claims Act against Williams and certain of its wholly owned subsidiaries, including those that owned Four Corners.and us. The claims sought an unspecified amount of royalties allegedly not paid to the federal government, treble damages, a civil penalty, attorneys’ fees, and costs. Grynberg has also filed claims against approximately 300 other energy companies alleging that the defendants violated the False Claims Act in connection with the measurement, royalty valuation and purchase of hydrocarbons. In 1999, the Department of Justice announced that it was declining to intervene in any of the Grynberg cases, including the action filed in federal court in Colorado against us. Also in 1999, the Panel on Multi-District Litigation transferred all of these cases, including those filed against us, to the federal court in Wyoming for pre-trial purposes. Grynberg’s measurement claims remain pending against us and the other defendants; the court previously dismissed Grynberg’s royalty valuation claims. In May 2005, the court-appointed special master entered a report which recommended that the claims against certain Williams’ subsidiaries, including us, be dismissed. On October 20, 2006, the court dismissed all claims against us. In November 2006, Grynberg filed his notice of appeals with the Tenth Circuit Court of Appeals. WeThe amount of any possible liability cannot be reasonably estimate or quantify any potential liability.estimated at this time.

unfavorable eventruling to occur, there exists the possibility of a material adverse impacteffect on the results of operations in the period in which the eventruling occurs. Management, including internal counsel, currently believes that the ultimate resolution of the foregoing matters, taken as a whole and after consideration of amounts accrued, insurance coverage, recovery from customers or other indemnification arrangements, will not have a materiallymaterial adverse effect upon our future financial position.

     Our reportable segments are strategic business units that offer different products and services. The segments are managed separately because each segment requires different industry knowledge, technology and marketing strategies.