<PAGE>

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                                    FORM 10-Q

          [X] QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
                      SECURITIES EXCHANGE ACT OF 1934

                  For the Quarterly Period Ended March 31, 2005
                                       OR

          [ ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE
                       SECURITIES EXCHANGE ACT OF 1934

          For the Transition Period from ______________ to _____________________

                         Commission File Number 0-13546

                               ------------------

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
              ----------------------------------------------------
             (Exact Name of Registrant as Specified in Its Charter)

                          Delaware                        41-1464066
           ------------------------------           ---------------------
            (State or Other Jurisdiction of            (I.R.S. Employer
            Incorporation or Organization)          Identification Number)

            Suite 100, One Post Oak Central              77056-4400
         2000 Post Oak Boulevard, Houston, TX            ----------
       ----------------------------------------          (Zip Code)
       (Address of Principal Executive Offices)

       Registrant's Telephone Number, Including Area Code: (713) 296-6000

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.

                                   YES [X] NO [ ]

<PAGE>

                         PART I - FINANCIAL INFORMATION

ITEM 1 - FINANCIAL STATEMENTS

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
                        STATEMENT OF CONSOLIDATED INCOME
                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                                      FOR THE THREE MONTHS
                                                         ENDED MARCH 31,
                                               ---------------------------------
                                                     2005              2004
                                               ---------------   ---------------
<S>                                            <C>               <C>
REVENUES:
    Oil and gas sales                          $     3,376,275   $     3,250,730
    Interest income                                     22,388             6,084
                                               ---------------   ---------------
                                                     3,398,663         3,256,814
                                               ---------------   ---------------

EXPENSES:
    Depreciation, depletion and amortization           567,036           689,206
    Asset retirement obligation accretion               12,601            11,922
    Lease operating costs                              307,921           198,610
    Gathering and transportation expense                42,824            34,992
    Administrative                                     107,000           102,000
                                               ---------------   ---------------
                                                     1,037,382         1,036,730
                                               ---------------   ---------------

NET INCOME                                     $     2,361,281   $     2,220,084
                                               ===============   ===============
NET INCOME ALLOCATED TO:
    Managing Partner                           $       568,413   $       564,279
    Investing Partners                               1,792,868         1,655,805
                                               ---------------   ---------------
                                               $     2,361,281   $     2,220,084
                                               ===============   ===============

NET INCOME PER INVESTING PARTNER UNIT          $         1,698   $         1,561
                                               ===============   ===============

WEIGHTED AVERAGE INVESTING PARTNER
  UNITS OUTSTANDING                                    1,055.7           1,060.7
                                               ===============   ===============
</TABLE>

                 The accompanying notes to financial statements
                     are an integral part of this statement.

                                       1
<PAGE>

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
                      STATEMENT OF CONSOLIDATED CASH FLOWS
                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                                                              FOR THE THREE MONTHS
                                                                                 ENDED MARCH 31,
                                                                          ----------------------------
                                                                              2005             2004
                                                                          ------------     -----------
<S>                                                                       <C>              <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
    Net income                                                            $  2,361,281     $ 2,220,084
    Adjustments to reconcile net income to net cash
       provided by operating activities:
          Depreciation, depletion and amortization                             567,036         689,206
          Asset retirement obligation accretion                                 12,601          11,922
          Dismantlement and abandonment cost                                         -        (146,222)
          Changes in operating assets and liabilities:
              (Increase) decrease in accrued revenues receivable               211,469          18,345
              (Increase) decrease in receivable from/payable to
                Apache Corporation                                              26,945         (97,855)
              Increase (decrease) in accrued operating expenses payable         25,033           6,049
                                                                          ------------     -----------
          Net cash provided by operating activities                          3,204,365       2,701,529
                                                                          ------------     -----------
CASH FLOWS FROM INVESTING ACTIVITIES:
    Additions to oil and gas properties                                         (9,744)       (198,621)
                                                                          ------------     -----------
          Net cash used in investing activities                                 (9,744)       (198,621)
                                                                          ------------     -----------

CASH FLOWS FROM FINANCING ACTIVITIES:
    Distributions to Investing Partners                                     (4,222,585)     (2,121,466)
    Distributions to Managing Partner                                         (631,006)       (581,420)
                                                                          ------------     -----------
          Net cash used in financing activities                             (4,853,591)     (2,702,886)
                                                                          ------------     -----------

NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                        (1,658,970)       (199,978)

CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR                                 3,333,640       2,271,495
                                                                          ------------     -----------

CASH AND CASH EQUIVALENTS, END OF PERIOD                                  $  1,674,670     $ 2,071,517
                                                                          ============     ===========
</TABLE>

                 The accompanying notes to financial statements
                     are an integral part of this statement.

                                       2
<PAGE>

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
                           CONSOLIDATED BALANCE SHEET
                                   (UNAUDITED)

<TABLE>
<CAPTION>
                                                                    MARCH 31,         DECEMBER 31,
                                                                       2005               2004
                                                                 ---------------    ---------------
<S>                                                              <C>                <C>
                                 ASSETS

CURRENT ASSETS:
   Cash and cash equivalents                                     $     1,674,670    $     3,333,640
   Accrued revenues receivable                                           753,852            965,321
   Receivable from Apache Corporation                                    138,529            165,474
                                                                 ---------------    ---------------
                                                                       2,567,051          4,464,435
                                                                 ---------------    ---------------

OIL AND GAS PROPERTIES, on the basis of full cost accounting:
   Proved properties                                                 184,075,346        184,065,602
   Less - Accumulated depreciation, depletion and amortization      (176,882,253)      (176,315,217)
                                                                 ---------------    ---------------
                                                                       7,193,093          7,750,385
                                                                 ---------------    ---------------
                                                                 $     9,760,144    $    12,214,820
                                                                 ===============    ===============

                    LIABILITIES AND PARTNERS' CAPITAL

CURRENT LIABILITIES:
   Accrued operating expenses                                    $        88,802    $        63,769
                                                                 ---------------    ---------------
                                                                          88,802             63,769
                                                                 ---------------    ---------------

ASSET RETIREMENT OBLIGATION                                              870,808            858,207
                                                                 ---------------    ---------------

PARTNERS' CAPITAL:
   Managing Partner                                                      145,029            207,621
   Investing Partners (1,055.7 units outstanding)                      8,655,505         11,085,223
                                                                 ---------------    ---------------
                                                                       8,800,534         11,292,844
                                                                 ---------------    ---------------
                                                                 $     9,760,144    $    12,214,820
                                                                 ===============    ===============
</TABLE>

                 The accompanying notes to financial statements
                     are an integral part of this statement.

                                       3
<PAGE>

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
                                   (UNAUDITED)

      The financial statements included herein have been prepared by the Apache
Offshore Investment Partnership (the Partnership), without audit, pursuant to
the rules and regulations of the Securities and Exchange Commission, and reflect
all adjustments which are, in the opinion of management, necessary for a fair
statement of the results for the interim periods, on a basis consistent with the
annual audited financial statements. All such adjustments are of a normal,
recurring nature. Certain information, accounting policies, and footnote
disclosures normally included in financial statements prepared in accordance
with generally accepted accounting principles have been omitted pursuant to such
rules and regulations, although the Partnership believes that the disclosures
are adequate to make the information presented not misleading. These financial
statements should be read in conjunction with the financial statements and the
summary of significant accounting policies and notes thereto included in the
Partnership's latest annual report on Form 10-K.

1.    RECEIVABLE FROM APACHE CORPORATION

      The receivable from Apache Corporation, the Partnership's managing partner
(Apache or the Managing Partner), represents the net result of the Investing
Partners' revenue and expenditure transactions in the current month. Generally,
cash in this amount will be paid by Apache to the Partnership in the month after
the Partnership's transactions are processed and the net results of operations
are determined.

2.    RIGHT OF PRESENTMENT

      As provided in the Partnership Agreement, as amended (the Amended
Partnership Agreement), a first right of presentment offer for 2005 of $12,418
per Unit, plus interest to the date of payment, was made to Investing Partners
in April 2005, based on a valuation date of December 31, 2004. The Investing
Partners had until April 30, 2005 to offer their Units under the current right
of presentment, and as of that date, the Partnership had been presented with .25
Units for repurchase under the current offer.

3.    ASSET RETIREMENT OBLIGATIONS

      The Partnership's increase in asset retirement obligations (ARO) liability
from December 31, 2004 was attributable to accretion expense of $12,601.

                                       4
<PAGE>

ITEM  2 - MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
          RESULTS OF OPERATIONS

RESULTS OF OPERATIONS

NET INCOME AND REVENUE

      The Partnership reported net income for the first quarter of 2005 of $2.4
million, up from earnings of $2.2 million in the first quarter 2004. Net income
per Investing Partner Unit increased nine percent from a year ago, rising from
$1,561 per Unit in the first quarter 2004 to $1,698 per Unit in the current
quarter. Higher oil and gas prices in the current period more than offset the
impact of lower production and higher operating costs. Total revenue increased
four percent from a year ago, rising from $3.3 million in the first quarter of
2004 to $3.4 million in the first quarter of 2005.

      The Partnership's oil and gas production volume and price information is
summarized in the following table (gas volumes presented in thousand cubic feet
(Mcf) per day):

<TABLE>
<CAPTION>
                                                     FOR THE THREE MONTHS
                                                        ENDED MARCH 31,
                                                     --------------------   INCREASE
                                                       2005       2004     (DECREASE)
                                                     --------  ----------  ---------
<S>                                                  <C>       <C>         <C>
Gas volume - Mcf per day                                3,472     3,750        (7%)
Average gas price - per Mcf                          $   6.71  $   5.99        12%
Oil volume - barrels per day                              253       338       (25%)
Average oil price - per barrel                       $  48.03  $  35.24        36%
Natural gas liquids (NGL) volume - barrels per day         66        48        38%
Average NGL price - per barrel                       $  30.80  $  27.54        12%
</TABLE>

OIL AND GAS SALES

      Natural gas sales for the first quarter of 2005 totaled $2.1 million, up
three percent from the first quarter of 2004. The Partnership's average realized
natural gas price for the first quarter of 2005 increased $.72 per Mcf from the
year-earlier period, increasing current sales by approximately $.2 million.
Natural gas volumes on a daily basis decreased seven percent from a year ago as
a result of natural depletion. Steep declines at Matagorda Island 681/682 and
South Timbalier 295 more than offset production added through drilling at Ship
Shoal 258/259 in 2004.

      The Partnership's crude oil sales for the first quarter of 2005 totaled
$1.1 million, a one percent increase from the first quarter of 2004. A $12.79
per barrel, or 36 percent, increase in the Partnership's average realized oil
price contributed to the increase in oil revenues. Oil production was 25 percent
lower than a year ago as a result of natural depletion at South Timbalier 295.

      The Partnership sold an average of 66 barrels per day of natural gas
liquids from processing gas during the first quarter of 2005, a 38 percent
increase over 2004.

      Declines in oil and gas production can be expected in future periods due
to natural depletion. Given the small number of producing wells owned by the
Partnership, and the fact that offshore wells tend to decline at a faster rate
than onshore wells, the Partnership's future production will be subject to more
volatility than those companies with more diversified wells and longer-lived
properties.

OPERATING EXPENSES

      The Partnership's depreciation, depletion and amortization (DD&A) rate,
expressed as a percentage of oil and gas sales, was approximately 17 percent
during the first quarter of 2005 compared to 21 percent during the same period
in 2004. The decline in rate in 2005 reflected higher prices in the current year
and reserve additions from drilling in 2004. During the first quarter, the
Partnership recognized $12,601 of accretion expense on the asset retirement
obligation.

      Lease operating expense for the first quarter of 2005 of $.3 million
increased 55 percent over the first quarter of 2004. The increase reflected
repair and maintenance costs on the North Padre Island 969/976 platform and
repair

                                       5
<PAGE>

costs at South Pass 83. The North Padre Island 969/976 work included replacement
of the platform decking, grating, handrails and gauges, while the South Pass 83
work was primarily for storm-related repairs. Administrative expense increased
slightly from the first quarter of 2004.

CAPITAL RESOURCES AND LIQUIDITY

      The Partnership's primary capital resource is net cash provided by
operating activities, which totaled $3.2 million for the first three months of
2005. Net cash provided by operating activities in the quarter was up 19 percent
from a year ago as a result of increases in oil and gas prices. Future cash
flows will be influenced by fluctuations in product prices, production levels
and operating costs.

      The Partnership's future financial condition, results of operations and
cash from operating activities will largely depend upon prices received for its
oil and natural gas production. A substantial portion of the Partnership's
production is sold under market-sensitive contracts. Prices for oil and natural
gas are subject to fluctuations in response to changes in supply, market
uncertainty and a variety of factors beyond the Partnership's control. These
factors include worldwide political instability (especially in the Middle East),
the foreign supply of oil and natural gas, the price of foreign imports, the
level of consumer demand, and the price and availability of alternative fuels.
With natural gas accounting for 64 percent of the Partnership's first quarter
2005 production and 57 percent of total proved reserves at December 31, 2004, on
an energy equivalent basis, the Partnership is affected more by fluctuations in
natural gas prices than in oil prices.

      The Partnership's oil and gas reserves and production will also
significantly impact future results of operations and cash from operating
activities. The Partnership's production is subject to fluctuations in response
to remaining quantities of oil and gas reserves, weather, pipeline capacity,
consumer demand, mechanical performance and workover, recompletion and drilling
activities. Declines in oil and gas production can be expected in future years
as a result of normal depletion and the Partnership not participating in
acquisition or exploration activities. Based on production estimates from
independent engineers and current market conditions, the Partnership expects it
will be able to meet its liquidity needs for routine operations in the
foreseeable future. The Partnership will reduce capital expenditures and
distributions to partners as cash from operating activities decline.

      In the event that future short-term operating cash requirements are
greater than the Partnership's financial resources, the Partnership may seek
short-term, interest-bearing advances from the Managing Partner as needed. The
Managing Partner, however, is not obligated to make loans to the Partnership.

      On an ongoing basis, the Partnership reviews the possible sale of lower
value properties prior to incurring associated dismantlement and abandonment
costs.

CAPITAL COMMITMENTS

      The Partnership's primary needs for cash are for operating expenses,
drilling and recompletion expenditures, future dismantlement and abandonment
costs, distributions to Investing Partners, and the purchase of Units offered by
Investing Partners under the right of presentment. The Partnership had no
outstanding debt or lease commitments at March 31, 2005. The Partnership did not
have any contractual obligations as of March 31, 2005, other than the liability
for dismantlement and abandonment costs of its oil and gas properties. The
Partnership has recorded a separate liability for the fair value of this asset
retirement obligation as discussed under the discussion of critical accounting
policies noted above.

      The Partnership did not participate in any new drilling or recompletion
projects during the first quarter of 2005 and did not have any drilling in
progress at December 31, 2004. The Partnership's oil and gas property
expenditures during the quarter were primarily for seismic costs.

      Based on information supplied by the operators of the properties, the
Partnership anticipates capital expenditures of approximately $.8 million for
the remainder of 2005, primarily for drilling the wells at Ship Shoal 258/259.
Such estimates may change based on realized prices, drilling results or changes
by the operator to the development plan.

      On March 17, 2005, the Partnership paid distributions to Investing
Partners totaling $4.2 million, or $4,000 per Investing Partner unit. The
Partnership made a cash distribution to Investing Partners during the first
quarter of 2004 of $2,000 per Investing Partner Unit. The amount of future
distributions will be dependent on actual and expected production levels,
realized and expected oil and gas prices, expected drilling and recompletion

                                       6
<PAGE>

expenditures, and prudent cash reserves for future dismantlement and abandonment
costs that will be incurred after the Partnership's reserves are depleted.

      As provided in the Amended Partnership Agreement, a first right of
presentment offer for 2005 of $12,418 per Unit was offered to Investing Partners
in April 2005, based on a valuation date of December 31, 2004. The Investing
Partners had until April 30, 2005 to offer their Units under the current right
of presentment, and as of that date, the Partnership had been presented with .25
Units for repurchase under the current offer.

ITEM 3 - QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

      The Partnership's major market risk exposure is in the pricing applicable
to its oil and gas production. Realized pricing is primarily driven by the
prevailing worldwide price for crude oil and spot prices applicable to its
natural gas production. Prices received for oil and gas production have been and
remain volatile and unpredictable. The Partnership has not used derivative
financial instruments or otherwise engaged in hedging activities during 2004 or
the first three months of 2005.

      The information set forth under "Commodity Risk" in Item 7A of the
Partnership's Form 10-K for the year ended December 31, 2004, is incorporated by
reference. Information about market risks for the current quarter is not
materially different.

ITEM 4 - CONTROLS AND PROCEDURES

      G. Steven Farris, the Managing Partner's President, Chief Executive
Officer and Chief Operating Officer, and Roger B. Plank, the Managing Partner's
Executive Vice President and Chief Financial Officer, evaluated the
effectiveness of the Partnership's disclosure controls and procedures as of the
end of the period covered by this report. Based on that evaluation and as of the
date of that evaluation, these officers concluded that the Partnership's
disclosure controls to be effective, providing effective means to insure that
information it is required to disclose under applicable laws and regulations is
recorded, processed, summarized and reported in a timely manner. Also, no
significant changes were made in the Partnership's internal controls over
financial reporting during the fiscal quarter ending March 31, 2005 that have
materially affected, or are reasonably likely to materially affect, the
Partnership's internal control over financial reporting.

FORWARD-LOOKING STATEMENTS AND RISK

      Certain statements in this report, including statements of the future
plans, objectives, and expected performance of the Partnership, are
forward-looking statements that are dependent on certain events, risks and
uncertainties that may be outside the Partnership's control, and which could
cause actual results to differ materially from those anticipated. Some of these
include, but are not limited to, the market prices of oil and gas, economic and
competitive conditions, inflation rates, legislative and regulatory changes,
financial market conditions, political and economic uncertainties of foreign
governments, future business decisions, and other uncertainties, all of which
are difficult to predict.

      There are numerous uncertainties inherent in estimating quantities of
proved oil and gas reserves and in projecting future rates of production and
timing of development expenditures. The total amount or timing of actual future
production may vary significantly from reserves and production estimates. The
drilling of exploratory wells can involve significant risks, including those
related to timing, success rates and cost overruns. Lease and rig availability,
complex geology and other factors can affect these risks. Fluctuations in oil
and gas prices, or a prolonged period of low prices, may substantially adversely
affect the Partnership's financial position, results of operations and cash
flows.

                                       7
<PAGE>

                           PART II - OTHER INFORMATION

ITEM 1.  LEGAL PROCEEDINGS

         None.

ITEM 2.  CHANGES IN SECURITIES, USE OF PROCEEDS AND ISSUER PURCHASES OF EQUITY
         SECURITIES

         None.

ITEM 3.  DEFAULTS UPON SENIOR SECURITIES

         None.

ITEM 4.  SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

         None.

ITEM 5.  OTHER INFORMATION

         None.

ITEM 6.  EXHIBITS AND REPORTS ON FORM 8-K

         a.  Exhibits

             31.1 - Certification of Chief Executive Officer

             31.2 - Certification of Chief Financial Officer

             32.1 - Certification of Chief Executive Officer and Chief Financial
                    Officer

         b.  Reports filed on Form 8-K - None.

                                       8
<PAGE>

                                   SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the registrant has duly caused this report to be signed on its
behalf by the undersigned thereunto duly authorized.

                                         APACHE OFFSHORE INVESTMENT PARTNERSHIP
                                         By: Apache Corporation, General Partner

Dated: May 9, 2005                       /s/ Roger B. Plank
                                         -------------------------------
                                         Roger B. Plank
                                         Executive Vice President and
                                         Chief Financial Officer

Dated: May 9, 2005                       /s/ Thomas L. Mitchell
                                         -------------------------------
                                         Thomas L. Mitchell
                                         Vice President and Controller
                                         (Chief Accounting Officer)

<PAGE>

                                 EXHIBIT INDEX

31.1 - Certification of Chief Executive Officer

31.2 - Certification of Chief Financial Officer

32.1 - Certification of Chief Executive Officer and Chief Financial Officer