<Page>
Filed by: Key Production Company, Inc.
This Communication is filed pursuant
to Rule 425 under the Securities Act
of 1933, as amended, and deemed
filed pursuant to Rule 14a-12 of the
Securities Exchange Act of 1934.
Subject Company: Key Production
Company, Inc.
Commission File Number: 001-11769
FORWARD LOOKING STATEMENTS
It should be noted that the following communication contains certain statements
that may be deemed to be "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. Such forward-looking statements
include, without limitation, statements regarding the consummation of the
proposed spin-off and merger, its effect on future earnings, cash flow or other
operating results, the expected closing date of the proposed spin-off and
merger, any other effect or benefit of the proposed spin-off and merger, the tax
treatment of the proposed spin-off and merger and the combined company, market
prospects, and any other statements that are not historical facts. H&P and Key
Production strongly encourage readers to note that some or all of the
assumptions upon which such forward-looking statements are based are beyond
their ability to control or estimate precisely, and may in some cases be subject
to rapid and material changes. Such assumptions include but are not limited to
costs and difficulties related to the integration of the businesses, costs,
delays and other difficulties related to the proposed spin-off and merger,
closing conditions not being satisfied, general market conditions prevailing in
the exploration for and development and production of oil and gas (including
inflation or lack of availability of goods and services, environmental risks,
drilling risks and regulatory changes), operating hazards and delays, actions by
customers and other third parties, the future price of oil and gas, and other
factors detailed in H&P's and Key Production's filings with the Securities and
Exchange Commission (the "SEC"), which are available free of charge on the SEC's
website at WWW.SEC.GOV. Should one or more of these risks or uncertainties
materialize, or should underlying assumptions prove incorrect, actual results
may vary materially from those indicated. H&P and Key Production undertake no
obligation to publicly update any forward-looking statements, whether as a
result of new information, future events or otherwise.
ADDITIONAL INFORMATION
In connection with the previously announced spin-off and merger involving the
exploration and production division of Helmerich & Payne, Inc. (H&P), Key
Production Company, Inc. (Key) and the company that has been formed to
receive the exploration and production assets of H&P, Cimarex Energy, Co.
(Cimarex), has filed a proxy statement/prospectus with the SEC and it will be
mailed to all security holders of Key. INVESTORS AND SECURITY HOLDERS ARE
URGED TO CAREFULLY READ THE PROXY STATEMENT/PROSPECTUS REGARDING THE PROPOSED
TRANSACTION WHEN IT BECOMES AVAILABLE, BECAUSE IT WILL CONTAIN IMPORTANT
INFORMATION. Investors and security holders may obtain a free copy of the
proxy statement/prospectus (when it is available) and other documents
containing information about Key Production and H&P's oil and gas division,
without charge, at the SEC's web site at www.sec.gov. Copies of the proxy
statement/prospectus and the SEC filings that will be incorporated by
reference in the proxy statement/prospectus may also be obtained for free by
directing a request to either: Key Production Company, Inc., 707 Seventeenth
Street, Suite 3300, Denver, Colorado 80202, Attention: Sharon M. Pope,
Assistant Corporate Secretary; telephone 303-295-3995, fax: 303-295-3494, or
Helmerich & Payne, Inc, Utica at Twenty-First Street, Tulsa, Oklahoma 74114,
<Page>
Attention: Steven R. Mackey, Corporate Secretary; telephone 918-742-5531, fax
918-743-2671.
PARTICIPANTS IN SOLICITATION
H&P, Cimarex, Key Production and their respective directors and executive
officers may be deemed to be participants in the solicitation of proxies from
Key Production's shareholders in connection with the proposed merger.
Information concerning Key Production's participants in the solicitation is set
forth in Key Production's proxy statement dated April 26, 2001, which is filed
with the SEC. Hans Helmerich, Douglas E. Fears and Steven R. Mackey are
currently directors of Cimarex, and each of them and Steven R. Shaw are
currently officers of Cimarex (the "Cimarex Participants"). None of the Cimarex
Participants beneficially owns any shares of Cimarex common stock. The Cimarex
Participants are all executive officers of H&P. Information concerning H&P's
participants in the solicitation is set forth in H&P's proxy statement dated
January 25, 2002, which is filed with the SEC. Key Production's shareholders may
obtain additional information about the interests of all such participants in
the proposed merger by reading the proxy statement/prospectus when it becomes
available. Investors should read the proxy statement/prospectus carefully when
it becomes available before making any voting or investment decisions.
<Page>
[H&P LOGO] [KEY LOGO]
CIMAREX ENERGY COMPANY
THE MERGER OF
HELMERICH & PAYNE'S E&P DIVISION
AND
KEY PRODUCTION COMPANY
Rocky Mountain Natural Gas Investment Forum
Denver, Colorado
August 7-8
<Page>
FORWARD-LOOKING STATEMENTS
This presentation contains certain "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. Such forward-looking
statements include, without limitation, statements regarding the consummation of
the proposed distribution and merger, its effect on future earnings, cash flow
or other operating results, any other effect or benefit of the proposed
distribution and merger, market prospects, and any other statements that are not
historical facts. H&P and Key strongly encourage readers to note that some or
all of the assumptions upon which such forward-looking statements are based are
beyond their ability to control or estimate precisely, and may in some cases be
subject to rapid and material changes. More detailed information about the
factors that could cause actual results to differ materially from those
described in the forward-looking statements is set forth in H&P and Key's
filings with the Securities and Exchange Commission, which are available free of
charge on the SEC's website at www.sec.gov. H&P and Key undertake no obligation
to publicly update any forward-looking statements discussed in this
presentation, whether as a result of new information, future events or
otherwise.
2
<Page>
ADDITIONAL INFORMATION
In connection with the proposed spin-off and merger, Key and Cimarex will file a
proxy statement/prospectus with the SEC. INVESTORS AND SECURITY HOLDERS ARE
URGED TO CAREFULLY READ THE PROXY STATEMENT/PROSPECTUS REGARDING THE PROPOSED
TRANSACTION WHEN IT BECOMES AVAILABLE, BECAUSE IT WILL CONTAIN IMPORTANT
INFORMATION. Investors and security holders may obtain a free copy of the proxy
statement/prospectus (when it is available) and other documents containing
information about Key and H&P's oil and gas division, without charge, at the
SEC's web site at www.sec.gov. Copies of the proxy statement/prospectus and the
SEC filings that will be incorporated by reference in the proxy
statement/prospectus may also be obtained for free by directing a request to
either: Key Production Company, Inc., 707 Seventeenth Street, Suite 3300,
Denver, Colorado 80202, Attention: Sharon M. Pope, Assistant Corporate
Secretary; telephone 303-295-3995, fax: 303-295-3494, or Helmerich & Payne,
Inc., Utica at Twenty-First Street, Tulsa, Oklahoma 74114, Attention: Steven R.
Mackey, Corporate Secretary; telephone 918-742-5531, fax: 918-743-2671.
PARTICIPANTS IN SOLICITATION
H&P, Cimarex, Key and their respective directors and executive officers may
be deemed to be participants in the solicitation of proxies from Key's
shareholders in connection with the proposed merger. Information concerning
Key's participants in the solicitation is set forth in Key's proxy statement
dated April 26, 2001, which is filed with the SEC. Hans Helmerich, Douglas E.
Fears and Steven R. Mackey are currently directors of Cimarex, and each of
them and Steven R. Shaw are currently officers of Cimarex (the "Cimarex
Participants"). None of the Cimarex Participants beneficially owns any shares
of Cimarex common stock. The Cimarex Participants are all executive officers
of H&P. Information concerning H&P's participants in the solicitation is set
forth in H&P's proxy statement dated January 25, 2002, which is filed with
the SEC. Key's shareholders may obtain additional information about the
interests of all such participants in the proposed merger by reading the
proxy statement/prospectus when it becomes available. Investors should read
the proxy statement/prospectus carefully when it becomes available before
making any voting or investment decisions.
3
<Page>
TRANSACTION SUMMARY
- - Merger of Key Production with H&P oil and gas division to create Cimarex
Energy Company
- - H&P shareholders - 65.25%;
Key shareholders - 34.75%
- - Structured as a tax-free spin / merge
- - Closing targeted for 3rd quarter 2002
4
<Page>
CIMAREX ENERGY AT A GLANCE
- - Proved reserves: 392 Bcfe (78% gas)
- - Production: 185 MMcfe per day
- Two-thirds Mid-Continent
- - Pro forma equity value: ~$700MM
- - Debt: $34MM
- - Proven track record
5
<Page>
BACKGROUND OF KEY
- - Founded in 1988 as the successor to Apache Petroleum Company, LP
- - Passive to active asset management in 1992
- - Objective: Consistent, profitable growth
- - Approach: Focus on drilling, measure progress on a per share basis
6
<Page>
KEY PRODUCTION - THEN AND NOW
<Table>
<Caption>
($ in millions) 1992 2001
- --------------------- ---- -----
Market Cap $25 $ 240
Debt $ 3 $ 34
Stock price ($/share) $ 3 $ 17
Reserves (Bcfe) 38 147
Reserves (Mcfe/share) 3.6 10.5
Production (Bcfe) 8.3 26.0
Gross Wells Drilled -- 107
</Table>
7
<Page>
WHY H&P?
- - High-quality asset base
- - High-margin, gas-oriented production
- - Good people
- - Production operations capacity
- - No debt
- - Similar drill bit strategies
8
<Page>
BASE PROPERTIES
[MAP]
HELMERICH & PAYNE, INC.
Proved reserves (Bcfe) 245
% Natural gas 87%
Production (MMcfe/d) 115
Net undeveloped acres 150,401
KEY PRODUCTION COMPANY
Proved reserves (Bcfe) 147
% Natural gas 62%
Production (MMcfe/d) 70
Net undeveloped acres 119,251
CIMAREX ENERGY COMPANY
Proved reserves (Bcfe) 392
% Natural gas 78%
Production (MMcfe/d) 185
Net undeveloped acres 269,652
9
<Page>
PROVED RESERVES
[PIE CHART]
BY REGION
Gulf Coast 13%
Kansas 21%
Western 23%
Mid-Continent 43%
[PIE CHART] [PIE CHART]
BY TYPE BY CATEGORY
Gas 78% PUD 2%
Oil 22% PD 98%
392 BCFE
10
<Page>
MID-CONTINENT OPERATIONS
KANSAS OKLA./N. TX
80 BCFE 169 BCFE
[MAP]
[PIE CHART] [PIE CHART]
Oil 14% Oil 15%
Gas 86% Gas 85%
[PIE CHART] [PIE CHART]
H&P 100% Key 47%
H&P 53%
11
<Page>
MID-CONTINENT / KS OVERLAP
OK / KS ACREAGE
H&P GROSS: 283,414
H&P NET: 153,144
[MAP]
KEY GROSS: 237,057
KEY NET: 78,669
Location of Properties
Helmerich & Payne
Key Production
Common Counties
12
<Page>
MID-CONTINENT EXPLORATION
[MAP]
KANSAS
50% WI
8 Wells
HEMPHILL / OTHER
75% WI
5 Wells
FOUR COUNTY AREA
50% WI
45 Wells
HARDEMAN
100% WI
12 Wells
ARKOMA
35% WI
15 Wells
13
<Page>
FOUR COUNTY AREA
[MAP]
- - Characteristics
- Multiple zones
- Low risk / high success rates
- High initial rates, long-lived reserves
- - Red Fork Wells
- CWC: $.8-1.6 MM
- Typical reserves: 1.5-5.0 Bcf
- - Atoka/Clinton Lake
- CWC: $2.5-2.8 MM
- Typical reserves: 2.0-6.0 Bcf
- - Granite Wash
- CWC: $.8-1.3 MM
- Typical reserves: 1.0-4.0 Bcf
14
<Page>
ANADARKO TYPE LOG
Des Moines Granite Wash
[CHART]
15
<Page>
HARDEMAN BASIN
[MAP]
- - 350 sq. miles of 3-D
- - 52 leads identified
- - Drilling Inventory
- 34 re-entry horizontal
- 9 pilot hole horizontal
- 9 vertical wells
- - Two rigs running
- - 2002 plans
- 8 re-entries
- 4 pilot holes
16
<Page>
HARDEMAN BASIN
HORIZONTAL WELLS
[CHART]
17
<Page>
KEY MID-CONTINENT PROGRESS
<Table>
<Caption>
1995 1996 1997 1998 1999 2000 2001
---- ---- ---- ---- ---- ---- ----
Wells Drilled 33 45 56 41 51 51 56
Success Rate 85% 89% 86% 76% 78% 80% 85%
% Operated 0% 2% 21% 34% 50% 65% 53%
Net Wells 1.0 6.6 11.7 13.2 16.0 24.4 24.3
Average WI 3% 43%
</Table>
18
<Page>
GULF COAST OPERATIONS
51 BCFE
[PIE CHART]
Oil 34%
Gas 66%
[PIE CHART]
Key 63%
H&P 37%
19
<Page>
GULF COAST EXPLORATION
ALLEN PARISH
50% WI
3 Wells
MS SALT BASIN
40% WI
5 Wells
JEFFERSON COUNTY
30% - 66% WI
6 Wells
COOK MOUNTAIN
50% WI
2 Wells
CAMERON PRAIRIE
13%-30% WI
6 Wells
LOBO
33% WI
3 Wells
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<Page>
MISSISSIPPI SALT BASIN
[MAP]
- - 14 salt domes
- - Eight 3-D seismic surveys
- - Established production at Centerville,
Kola, Monticello, Arm and Eminence
21
<Page>
MISSISSIPPI SALT BASIN
[MAP]
- - Multiple Objectives:
- Rodessa, Sligo, Hosston, Cotton Valley
- - Target Reserves: 3-7 Bcf/Well
- - Depth: 15,000-17,500 ft
- - D&C Cost: $2.2-3.0 MM
- - Avg. WI: 40%
22
<Page>
PERMIAN / WESTERN OPERATIONS
92 BCFE
Oil 35%
Gas 65%
[MAP]
Key 39%
H&P 61%
23
<Page>
2002 CAPITAL BUDGET
<Table>
<Caption>
($ in millions) H&P Key Total
- ------------------ ----- ----- -------
Mid-Continent $ 10 $ 34 $ 44
Gulf Coast 39 16 55
Permian / Western 6 8 14
----- ----- -------
Total $ 55 $ 58 $ 113
</Table>
24
<Page>
EQUITY MARKET CAP
[BAR CHART]
25
<Page>
CIMAREX ENERGY RECAP
- - New independent with critical mass of people and assets
- - Limited debt and substantial financial capacity
- - Predominantly Mid-Continent production base
- - Gulf Coast and Mid-Continent oriented exploration programs
26