<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 September 30, 2001

                                       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 INCOME
                                   (UNAUDITED)

<Table>
<Caption>
                                                        FOR THE QUARTER               FOR THE NINE MONTHS
                                                       ENDED SEPTEMBER 30,             ENDED SEPTEMBER 30,
                                                  ---------------------------       ---------------------------
                                                     2001             2000             2001            2000
                                                  ----------       ----------       ----------       ----------
<S>                                               <C>              <C>              <C>              <C>
REVENUES:
   Oil and gas sales                              $2,042,605       $3,315,497       $8,800,879       $8,858,213
   Interest income                                    25,368           42,477           65,434          108,944
                                                  ----------       ----------       ----------       ----------

                                                   2,067,973        3,357,974        8,866,313        8,967,157
                                                  ----------       ----------       ----------       ----------

EXPENSES:
   Depreciation, depletion and amortization          457,930          805,759        1,690,117        2,223,823
   Lease operating expense                           150,352          110,258          437,133          374,071
   Administrative                                    109,000          134,973          370,000          405,000
                                                  ----------       ----------       ----------       ----------

                                                     717,282        1,050,990        2,497,250        3,002,894
                                                  ----------       ----------       ----------       ----------

NET INCOME                                        $1,350,691       $2,306,984       $6,369,063       $5,964,263
                                                  ==========       ==========       ==========       ==========

NET INCOME ALLOCATED TO:
   Managing Partner                               $  332,847       $  571,244       $1,502,012       $1,497,173
   Investing Partners                              1,017,844        1,735,740        4,867,051        4,467,090
                                                  ----------       ----------       ----------       ----------

                                                  $1,350,691       $2,306,984       $6,369,063       $5,964,263
                                                  ==========       ==========       ==========       ==========

NET INCOME PER INVESTING PARTNER UNIT             $      907       $    1,537       $    4,324       $    3,948
                                                  ==========       ==========       ==========       ==========

WEIGHTED AVERAGE INVESTING PARTNER
   UNITS OUTSTANDING                                 1,122.3          1,129.5          1,125.7          1,131.4
                                                  ==========       ==========       ==========       ==========
</Table>


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

                                        1
<PAGE>

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
                             STATEMENT OF CASH FLOWS
                                   (UNAUDITED)

<Table>
<Caption>
                                                                               FOR THE NINE MONTHS ENDED
                                                                                      SEPTEMBER 30,
                                                                             ------------------------------
                                                                                2001               2000
                                                                             -----------        -----------
<S>                                                                          <C>                <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
   Net income                                                                $ 6,369,063        $ 5,964,263
   Adjustments to reconcile net income to net cash
      provided by operating activities:
         Depreciation, depletion and amortization                              1,690,117          2,223,823
         Changes in operating assets and liabilities:
             (Increase) decrease in accrued revenues receivable                  404,760           (129,164)
             Increase (decrease) in accrued operating expenses payable            22,341            (56,344)
             (Increase) decrease in receivable from/payable to
                 Apache Corporation                                             (563,347)           177,651
                                                                             -----------        -----------

         Net cash provided by operating activities                             7,922,934          8,180,229
                                                                             -----------        -----------

CASH FLOWS FROM INVESTING ACTIVITIES:
   Additions to oil and gas properties                                        (2,858,034)        (2,778,436)
   Non-cash portion of oil and gas property additions                            566,398           (202,851)
                                                                             -----------        -----------

         Net cash used in investing activities                                (2,291,636)        (2,981,287)
                                                                             -----------        -----------

CASH FLOWS FROM FINANCING ACTIVITIES:
   Repurchase of Partnership Units                                               (64,226)           (28,047)
   Distributions to Investing Partners                                        (2,256,977)        (2,264,978)
   Distributions to Managing Partner, net                                     (1,575,551)        (1,477,889)
                                                                             -----------        -----------

         Net cash used in financing activities                                (3,896,754)        (3,770,914)
                                                                             -----------        -----------

NET INCREASE IN CASH AND CASH EQUIVALENTS                                      1,734,544          1,428,028

CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR                                   1,442,878          2,748,812
                                                                             -----------        -----------

CASH AND CASH EQUIVALENTS, END OF PERIOD                                     $ 3,177,422        $ 4,176,840
                                                                             ===========        ===========
</Table>


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

                                        2
<PAGE>

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
                                  BALANCE SHEET
                                   (UNAUDITED)

<Table>
<Caption>
                                                                     SEPTEMBER 30,         DECEMBER 31,
                                                                         2001                 2000
                                                                     -------------        -------------
<S>                                                                  <C>                  <C>
                                  ASSETS

CURRENT ASSETS:
   Cash and cash equivalents                                         $   3,177,422        $   1,442,878
   Accrued revenues receivable                                             619,538            1,024,298
   Receivable from Apache Corporation                                      172,092                   --
                                                                     -------------        -------------
                                                                         3,969,052            2,467,176
                                                                     -------------        -------------

OIL AND GAS PROPERTIES, on the basis of full cost accounting:
   Proved properties                                                   176,236,430          173,378,396
   Less - Accumulated depreciation, depletion and amortization        (168,820,210)        (167,130,093)
                                                                     -------------        -------------
                                                                         7,416,220            6,248,303
                                                                     -------------        -------------

                                                                     $  11,385,272        $   8,715,479
                                                                     =============        =============

                    LIABILITIES AND PARTNERS' CAPITAL

CURRENT LIABILITIES:
   Distributions payable                                             $   2,244,643        $          --
   Accrued exploration and development                                   1,077,398              511,000
   Accrued operating expenses payable and other                            107,125               84,784
   Payable to Apache Corporation                                                --              391,255
                                                                     -------------        -------------
                                                                         3,429,166              987,039
                                                                     -------------        -------------

PARTNERS' CAPITAL:
   Managing Partner                                                        278,542              352,081
   Investing Partners (1,122.3 and 1,128.5 units outstanding,
      respectively)                                                      7,677,564            7,376,359
                                                                     -------------        -------------
                                                                         7,956,106            7,728,440
                                                                     -------------        -------------
                                                                     $  11,385,272        $   8,715,479
                                                                     =============        =============
</Table>


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

                                        3

<PAGE>

                     APACHE OFFSHORE INVESTMENT PARTNERSHIP
                          NOTES TO 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/PAYABLE TO APACHE CORPORATION

     Receivable from/payable to 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 transferred from/to Apache 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 2001 of $9,928
per Unit, plus interest to the date of the payment, was made to Investing
Partners based on a valuation date of December 31, 2000. As a result, the
Partnership purchased 6.2 Units in June 2001 for a total of $64,226 in cash. A
second right of presentment offer for 2001 of $10,460 per Unit, plus interest to
the date of payment, was made to the Investing Partners on October 26, 2001,
based on a valuation date of June 30, 2001. The Unit holders have until the
close of business on November 26, 2001 to present their Units for repurchase by
the Partnership. The Partnership will determine by December 14, 2001, whether or
not to accept each Unit offered during this election period.

     The Partnership is not in a position to predict how many Units will be
presented for repurchase during the fourth quarter of 2001 and cannot, at this
time, determine if the Partnership will have sufficient funds available to
purchase Units. The Partnership has no obligation to purchase any Units
presented to the extent it determines that it has insufficient funds for such
purchases. The Amended Partnership Agreement contains limitations on the number
of Units that the Partnership can repurchase, including a limit of 10 percent of
the outstanding Units on an annual basis.


                                       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 in the third quarter of 2001 of $1.4
million, down from the prior year earnings of $2.3 million. Net income per
Investing Partner Unit decreased 41 percent, from $1,537 per Unit to $907 per
Unit.

     For the first nine months of 2001, net income totaled $6.4 million, or
$4,324 per Investing Partner Unit, up seven percent and 10 percent,
respectively, from $6 million, or $3,948 per Investing Partner Unit, in the same
period last year. The increases were attributable to higher average natural gas
prices during the first nine months of 2001 and the Partnership's lower
depreciation, depletion and amortization (DD&A) expense in 2001.

     Revenues for the quarter decreased 38 percent, falling from $3.4 million in
the third quarter of 2000 to $2.1 million in the third quarter of 2001. For the
first nine months of 2001, revenues decreased one percent to $8.9 million as
declines in production more than offset the impact of higher average gas prices.
Natural gas sales accounted for 74 percent of the Partnership's total revenues
during the first nine months of 2001 compared to 69 percent during the first
nine months of 2000.

     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 QUARTER ENDED SEPTEMBER 30,     FOR THE NINE MONTHS ENDED SEPTEMBER 30,
                                 -----------------------------------     ---------------------------------------
                                                         INCREASE                                   INCREASE
                                   2001       2000      (DECREASE)           2001        2000      (DECREASE)
                                 -------     ------     ----------          ------      -------    ----------
<S>                              <C>         <C>        <C>                <C>          <C>        <C>
Gas volume - Mcf per day           4,838       6,147       (21%)             4,792        6,678      (28%)
Average gas price - per Mcf      $  2.91     $  4.26       (32%)           $  5.02      $  3.38       49%
Oil volume - barrels per day         313         313        --                 304          333       (9%)
Average oil price - per barrel   $ 25.94     $ 31.50       (18%)           $ 26.92      $ 29.39       (8%)
</Table>

THIRD QUARTER 2001 COMPARED TO THIRD QUARTER 2000

     Natural gas production revenues for the third quarter of 2001 totaled $1.3
million, down 46 percent from the third quarter of 2000. Natural gas prices
decreased 32 percent for the third quarter of 2001 compared to the year-earlier
period. Natural gas volumes for the quarter declined 21 percent from a year ago
primarily due to natural production declines at East Cameron Block 60 and
Matagorda Island Block 681.

     The Partnership's crude oil production revenues for the third quarter of
2001 totaled $748,000, an 18 percent decrease from the third quarter of 2000.
The $.2 million decrease in oil sales was attributable to an 18 percent decrease
in average realized oil price, while crude oil production remained about the
same. Production added from drilling at the South Timbalier Block 295 was offset
by natural depletion.

YEAR-TO-DATE 2001 COMPARED TO YEAR-TO-DATE 2000

     Gas sales for the first nine months of 2001 of $6.6 million increased $.4
million, or six percent, when compared to the same period in 2000. Average
realized gas prices increased $1.64 per Mcf when compared with the first nine
months of 2000, positively impacting sales by $3.0 million. Daily gas production
for the first nine months of 2001 decreased by 28 percent when compared to the
same period in 2000, negatively impacting revenues by $2.6 million. Production
decreases in 2001 were primarily due to natural declines in production at East
Cameron Block 60, South Timbalier Block 295 and Matagorda Island Block 681.

     For the nine months ended September 30, 2001, oil sales decreased 17
percent to $2.2 million when compared to the same period last year. The
Partnership's oil sales revenues were unfavorably impacted by a nine percent
decrease in daily oil production and an eight percent decrease in realized
prices.


                                       5
<PAGE>

EXPENSES

     The Partnership's DD&A rate, expressed as a percentage of oil and gas
production revenues, was approximately 22 percent during the third quarter of
2001 compared to 24 percent during the same period in 2000. For the first nine
months, the Partnership's DD&A rate declined from 25 percent in 2000 to 19
percent in the current year. The decreases in the DD&A rates as a percentage of
sales were primarily a result of higher average natural gas prices in 2001 and
upward reserve revisions recognized at the end of 2000.

     Lease operating expense (LOE) in the third quarter 2001 was up
approximately $40,000 from the third quarter 2000 due to increases in repair
costs and maintenance. For the first nine months of 2001, LOE of $.4 million was
up 17 percent from a year ago due to higher maintenance and workover costs in
2001, and the receipt of an audit exception refund from an outside operator in
2000 which reduced last year's reported cost.

CASH FLOW, LIQUIDITY AND CAPITAL RESOURCES

CAPITAL RESOURCES AND LIQUIDITY

     The Partnership's primary capital resource is net cash provided by
operating activities, which was $7.9 million for the first nine months of 2001.
Net cash provided by operating activities in 2001 was down three percent from a
year ago as lower production and higher workover costs more than offset the
impact of higher average gas prices. Future cash flows will be influenced by
fluctuations in product prices, production levels and operating costs.

CAPITAL COMMITMENTS

     The Partnership's primary needs for cash are for operating expenses,
drilling and recompletion expenditures, distributions to Investing Partners, and
the purchase of Units offered by Investing Partners under the right of
presentment.

     During the first nine months of 2001, the Partnership's oil and gas
property additions totaled $2.9 million, which primarily related to drilling and
recompletion projects at South Timbalier Block 295. The Partnership participated
in the South Timbalier Block 295 A-13 sidetrack well drilled during the first
quarter of 2001 and the A-32 well on the block during the second quarter of this
year. The South Timbalier Block 295 A-10 ST H1 was drilled during the third
quarter. All three wells were completed as producers. The Partnership
anticipates capital expenditures of approximately $.2 million for the remainder
of 2001. Such estimates may change based on realized prices, drilling results or
changes by the operator to the development plan.

     The Partnership made a distribution to Investing Partners of $2,000 per
Unit on March 1, 2001 and $2,000 per Unit on October 5, 2001. 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
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 2001 of $9,928 per Unit, plus interest to the date of
payment, was made to Investing Partners, based on a valuation date of December
31, 2000. As a result, the Partnership purchased 6.2 Units in June 2001 for a
total of $64,226 in cash. A second right of presentment offer for 2001 of
$10,460 per Unit, plus interest to the date of payment, was made to Investing
Partners on October 26, 2001, based on a valuation date of June 30, 2001. The
Partnership is not in a position to predict how many Units will be presented for
repurchase during the fourth quarter of 2001 and cannot, at this time, determine
if the Partnership will have sufficient funds available to repurchase Units. The
Partnership has no obligation to purchase any Units presented to the extent it
determines that it has insufficient funds for such purchases. The Amended
Partnership Agreement contains limitations on the number of Units that the
Partnership can repurchase, including a limit of 10 percent of the outstanding
Units on an annual basis.


                                       6
<PAGE>

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.

COMMODITY 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. Historically, prices received for oil and gas production
have been volatile and unpredictable and price volatility is expected to
continue. The Partnership has not used derivative financial instruments or
otherwise engaged in hedging activities during 2000 or 2001.


                                       7
<PAGE>

PART II - OTHER INFORMATION

ITEM 1.      LEGAL PROCEEDINGS

             None.

ITEM 2.      CHANGES IN 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 - None.

             b. Reports 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:    November 12, 2001             /s/ Roger B. Plank
                                        ---------------------------------------
                                        Roger B. Plank
                                        Executive Vice President and Chief
                                        Financial Officer


Dated:    November 12, 2001             /s/ Thomas L. Mitchell
                                        ---------------------------------------
                                        Thomas L. Mitchell
                                        Vice President and Controller
                                        (Chief Accounting Officer)