<PAGE>   1
                       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, 2000

                                       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 0-21518

                            IEA INCOME FUND XII, L.P.
             (Exact name of registrant as specified in its charter)


            California                                          94-3143940
  (State or other jurisdiction of                           (I.R.S. Employer
  incorporation or organization)                           Identification No.)


         444 Market Street, 15th Floor, San Francisco, California      94111
                   (Address of principal executive offices)          (Zip Code)

                                 (415) 677-8990
              (Registrant's telephone number, including area code)


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>   2
                            IEA INCOME FUND XII, L.P.

                  REPORT ON FORM 10-Q FOR THE QUARTERLY PERIOD
                              ENDED MARCH 31, 2000

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>


                                                                                                       PAGE
<S>      <C>                                                                                           <C>
PART I - FINANCIAL INFORMATION

 Item 1. Financial Statements


         Condensed Balance Sheets - March 31, 2000 and December 31, 1999 (unaudited)                              4


         Condensed Statements of Operations for the three months ended March 31, 2000 and 1999 (unaudited)        5


         Condensed Statements of Cash Flows for the three months ended March 31, 2000 and 1999 (unaudited)        6


         Notes to Condensed Financial Statements (unaudited)                                                      7


 Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations                   10


 Item 3. Quantitative and Qualitative Disclosures About Market Risk                                              11


PART II - OTHER INFORMATION


 Item 6. Exhibits and Reports on Form 8-K                                                                        12
</TABLE>

                                       2

<PAGE>   3
                         PART I - FINANCIAL INFORMATION


 Item 1. Financial Statements

         Presented herein are the Registrant's condensed balance sheets as of
         March 31, 2000 and December 31, 1999, condensed statements of
         operations for the three months ended March 31, 2000 and 1999, and
         condensed statements of cash flows for the three months ended March 31,
         2000 and 1999.

                                       3

<PAGE>   4
                          IEA INCOME FUND XII, L.P.

                           CONDENSED BALANCE SHEETS

                                 (UNAUDITED)

<TABLE>
<CAPTION>
                                                                              March 31,        December 31,
                                                                                2000               1999
                                                                            ------------       ------------
<S>                                                                         <C>                <C>

                 Assets

Current assets:
   Cash and cash equivalents, includes $1,160,889 at March 31, 2000
      and $1,111,325 at December 31, 1999 in interest-bearing accounts      $  1,161,034       $  1,111,425
   Net lease receivables due from Leasing Company
      (notes 1 and 2)                                                            291,211            585,156
                                                                            ------------       ------------

         Total current assets                                                  1,452,245          1,696,581
                                                                            ------------       ------------


Container rental equipment, at cost                                           61,594,143         61,857,061
   Less accumulated depreciation                                              26,940,034         26,191,802
                                                                            ------------       ------------
      Net container rental equipment                                          34,654,109         35,665,259
                                                                            ------------       ------------

         Total assets                                                       $ 36,106,354       $ 37,361,840
                                                                            ============       ============

            Liabilities and Partners' Capital

Current liabilities:
   Accrued expenses                                                         $    229,050       $    254,500
                                                                            ------------       ------------


Partners' capital (deficit):
   General partner                                                              (128,494)          (116,193)
   Limited partners                                                           36,005,798         37,223,533
                                                                            ------------       ------------

         Total partners' capital                                              35,877,304         37,107,340
                                                                            ------------       ------------

         Total liabilities and partners' capital                            $ 36,106,354       $ 37,361,840
                                                                            ============       ============
</TABLE>


              The accompanying notes are an integral part of these
                        condensed financial statements.

                                       4

<PAGE>   5

                            IEA INCOME FUND XII, L.P.

                       CONDENSED STATEMENTS OF OPERATIONS

                                   (UNAUDITED)

<TABLE>
<CAPTION>


                                                                Three Months Ended
                                                           -----------------------------
                                                            March 31,         March 31,
                                                               2000              1999
                                                           -----------       -----------
<S>                                                        <C>               <C>
Net lease revenue (notes 1 and 3)                          $   954,521       $ 1,093,475

Other operating expenses:
  Depreciation                                                 905,763           915,896
  Other general and administrative expenses                     30,483            32,951
                                                           -----------       -----------
                                                               936,246           948,847
                                                           -----------       -----------

    Income from operations                                      18,275           144,628

Other income (loss):
  Interest income                                               14,719            23,953
  Net loss on disposal of equipment                            (40,776)          (92,685)
                                                           -----------       -----------
                                                               (26,057)          (68,732)
                                                           -----------       -----------

    Net income (loss)                                      $    (7,782)      $    75,896
                                                           ===========       ===========

Allocation of net income (loss):
  General partner                                          $    38,756       $    48,547
  Limited partners                                             (46,538)           27,349
                                                           -----------       -----------

                                                           $    (7,782)      $    75,896
                                                           ===========       ===========

Limited partners' per unit share of net income (loss)      $     (0.01)      $      0.01
                                                           ===========       ===========
</TABLE>

              The accompanying notes are an integral part of these
                        condensed financial statements.



                                       5

<PAGE>   6

                            IEA INCOME FUND XII, L.P.

                       CONDENSED STATEMENTS OF CASH FLOWS

                                   (UNAUDITED)

<TABLE>
<CAPTION>


                                                                      Three Months Ended
                                                                -----------------------------
                                                                 March 31,         March 31,
                                                                    2000              1999
                                                                -----------       -----------
<S>                                                             <C>               <C>
Net cash provided by operating activities                       $ 1,195,206       $ 1,087,115

Cash flows provided by (used in) investing activities:
  Proceeds from disposal of equipment                                76,656           154,371
  Purchase of container rental equipment                                 --          (199,342)
  Acquisition fees paid to general partner                               --            (9,967)
                                                                -----------       -----------

       Net cash provided by (used in) investing activities           76,656           (54,938)
                                                                -----------       -----------

Cash flows used in financing activities:
  Distribution to partners                                       (1,222,253)       (1,290,450)
                                                                -----------       -----------

Net increase (decrease) in cash and cash equivalents                 49,609          (258,273)

Cash and cash equivalents at January 1                            1,111,425         2,407,614
                                                                -----------       -----------

Cash and cash equivalents at March 31                           $ 1,161,034       $ 2,149,341
                                                                ===========       ===========
</TABLE>

              The accompanying notes are an integral part of these
                        condensed financial statements.

                                       6

<PAGE>   7

                            IEA INCOME FUND XII, L.P.

               NOTES TO UNAUDITED CONDENSED FINANCIAL STATEMENTS


(1)  Summary of Significant Accounting Policies

     (a) Nature of Operations

         IEA Income Fund XII, L.P. (the "Partnership") is a limited partnership
         organized under the laws of the State of California on August 28, 1991
         for the purpose of owning and leasing marine cargo containers worldwide
         to ocean carriers. To this extent, the Partnership's operations are
         subject to the fluctuations of world economic and political conditions.
         Such factors may affect the pattern and levels of world trade. The
         Partnership believes that the profitability of, and risks associated
         with, leases to foreign customers is generally the same as those of
         leases to domestic customers. The Partnership's leases generally
         require all payments to be made in United States currency.

         Cronos Capital Corp. ("CCC") is the general partner and, with its
         affiliate Cronos Containers Limited (the "Leasing Company"), manages
         the business of the Partnership. CCC and the Leasing Company also
         manage the container leasing business for other partnerships affiliated
         with the general partner. The Partnership shall continue until December
         31, 2011, unless sooner terminated upon the occurrence of certain
         events.

         The Partnership commenced operations on January 31, 1992, when the
         minimum subscription proceeds of $2,000,000 were obtained. The
         Partnership offered 3,750,000 units of limited partnership interest at
         $20 per unit, or $75,000,000. The offering terminated on November 30,
         1992, at which time 3,513,594 limited partnership units had been
         purchased.

     (b) Leasing Company and Leasing Agent Agreement

         The Partnership has entered into a Leasing Agent Agreement whereby the
         Leasing Company has the responsibility to manage the leasing operations
         of all equipment owned by the Partnership. Pursuant to the Agreement,
         the Leasing Company is responsible for leasing, managing and re-leasing
         the Partnership's containers to ocean carriers, and has full discretion
         over which ocean carriers and suppliers of goods and services it may
         deal with. The Leasing Agent Agreement permits the Leasing Company to
         use the containers owned by the Partnership, together with other
         containers owned or managed by the Leasing Company and its affiliates,
         as part of a single fleet operated without regard to ownership. Since
         the Leasing Agent Agreement meets the definition of an operating lease
         in Statement of Financial Accounting Standards (SFAS) No. 13, it is
         accounted for as a lease under which the Partnership is lessor and the
         Leasing Company is lessee.

         The Leasing Agent Agreement generally provides that the Leasing Company
         will make payments to the Partnership based upon rentals collected from
         ocean carriers after deducting direct operating expenses and management
         fees to CCC and the Leasing Company. The Leasing Company leases
         containers to ocean carriers, generally under operating leases which
         are either master leases or term leases (mostly one to five years).
         Master leases do not specify the exact number of containers to be
         leased or the term that each container will remain on hire but allow
         the ocean carrier to pick up and drop off containers at various
         locations; rentals are based upon the number of containers used and the
         applicable per-diem rate. Accordingly, rentals under master leases are
         all variable and contingent upon the number of containers used. Most
         containers are leased to ocean carriers under master leases; leasing
         agreements with fixed payment terms are not material to the financial
         statements. Since there are no material minimum lease rentals, no
         disclosure of minimum lease rentals is provided in these condensed
         financial statements.

                                       7

<PAGE>   8
                            IEA INCOME FUND XII, L.P.

               NOTES TO UNAUDITED CONDENSED FINANCIAL STATEMENTS


     (c) Basis of Accounting

         The Partnership utilizes the accrual method of accounting. Net lease
         revenue is recorded by the Partnership in each period based upon its
         leasing agent agreement with the Leasing Company. Net lease revenue is
         generally dependent upon operating lease rentals from operating lease
         agreements between the Leasing Company and its various lessees, less
         direct operating expenses and management fees due in respect of the
         containers specified in each operating lease agreement.

     (d) Financial Statement Presentation

         These condensed financial statements have been prepared without audit.
         Certain information and footnote disclosures normally included in
         financial statements prepared in accordance with generally accepted
         accounting procedures have been omitted. It is suggested that these
         condensed financial statements be read in conjunction with the
         financial statements and accompanying notes in the Partnership's latest
         annual report on Form 10-K.

         The preparation of financial statements in conformity with accounting
         principles generally accepted in the United States (GAAP) requires the
         Partnership to make estimates and assumptions that affect the reported
         amounts of assets and liabilities and disclosure of contingent assets
         and liabilities at the date of the financial statements and the
         reported amounts of revenues and expenses during the reported period.
         Actual results could differ from those estimates.

         The interim financial statements presented herewith reflect all
         adjustments of a normal recurring nature which are, in the opinion of
         management, necessary to a fair statement of the financial condition
         and results of operations for the interim periods presented. The
         results of operations for such interim periods are not necessarily
         indicative of the results to be expected for the full year.


(2)  Net Lease Receivables Due from Leasing Company

     Net lease receivables due from the Leasing Company are determined by
     deducting direct operating payables and accrued expenses, base management
     fees payable, and reimbursed administrative expenses payable to CCC and its
     affiliates from the rental billings payable by the Leasing Company to the
     Partnership under operating leases to ocean carriers for the containers
     owned by the Partnership. Net lease receivables at March 31, 2000 and
     December 31, 1999 were as follows:

<TABLE>
<CAPTION>

                                                      March 31,        December 31,
                                                         2000              1999
                                                    -------------      -------------
<S>                                                 <C>                <C>
Gross lease receivables                             $   1,709,487      $   1,676,207
Less:
Direct operating payables and accrued expenses            682,789            432,023
Damage protection reserve                                 181,060            189,163
Base management fees payable                              244,819            271,648
Reimbursed administrative expenses                         69,837             33,911
Allowance for doubtful accounts                           239,771            164,306
                                                    -------------      -------------
Net lease receivables                               $     291,211      $     585,156
                                                    =============      =============
</TABLE>


                                       8
<PAGE>   9
                            IEA INCOME FUND XII, L.P.

               NOTES TO UNAUDITED CONDENSED FINANCIAL STATEMENTS


(3)  Net Lease Revenue

     Net lease revenue is determined by deducting direct operating expenses,
     base management fees and reimbursed administrative expenses to CCC and its
     affiliates from the rental revenue billed by the Leasing Company under
     operating leases to ocean carriers for the containers owned by the
     Partnership. Net lease revenue for the three-month periods ended March 31,
     2000 and 1999 were as follows:

<TABLE>
<CAPTION>

                                                Three Months Ended
                                         --------------------------------
                                            March 31,          March 31,
                                              2000               1999
                                         -------------      -------------
<S>                                      <C>                <C>
Rental revenue (note 4)                  $   1,759,088      $   1,862,426
Less:
Rental equipment operating expenses            565,073            537,698
Base management fees                           115,990            128,266
Reimbursed administrative expenses             123,504            102,987
                                         -------------      -------------

                                         $     954,521      $   1,093,475
                                         =============      =============
</TABLE>


(4)  Operating Segment

     The Financial Accounting Standards Board has issued SFAS No. 131,
     "Disclosures about Segments of an Enterprise and Related Information,"
     which changes the way public business enterprises report financial and
     descriptive information about reportable operating segments. An operating
     segment is a component of an enterprise that engages in business activities
     from which it may earn revenues and incur expenses, whose operating results
     are regularly reviewed by the enterprise's chief operating decision maker
     to make decisions about resources to be allocated to the segment and assess
     its performance, and about which separate financial information is
     available. Management operates the Partnership's container fleet as a
     homogenous unit and has determined, after considering the requirements of
     SFAS No. 131, that as such it has a single reportable operating segment.

     The Partnership derives its revenues from marine cargo containers. As of
     March 31, 2000, the Partnership operated 9,174 twenty-foot, 5,142
     forty-foot and 204 forty-foot high-cube marine dry cargo containers, as
     well as 195 twenty-foot and 289 forty-foot marine refrigerated cargo
     containers. A summary of gross lease revenue, by product, for the
     three-month periods ended March 31, 2000 and 1999 follows:

<TABLE>
<CAPTION>

                                 Three Months Ended
                             ----------------------------
                              March 31,         March 31,
                                2000             1999
                             -----------      -----------
<S>                          <C>              <C>
Dry cargo containers         $ 1,422,865      $ 1,489,917
Refrigerated containers          336,223          372,509
                             -----------      -----------

Total                        $ 1,759,088      $ 1,862,426
                             ===========      ===========
</TABLE>

     Due to the Partnership's lack of information regarding the physical
     location of its fleet of containers when on lease in the global shipping
     trade, it is impracticable to provide the geographic area information
     required by SFAS No. 131.


                                     ******


                                       9

<PAGE>   10

Item 2. Management's Discussion and Analysis of Financial Condition and Results
        of Operations


It is suggested that the following discussion be read in conjunction with the
Registrant's most recent annual report on Form 10-K.

1)   Material changes in financial condition between March 31, 2000 and December
     31, 1999.

     At March 31, 2000, the Registrant had $1,161,034 in cash and cash
     equivalents, an increase of $49,609 from the cash balances at December 31,
     1999.

     The Registrant's allowance for doubtful accounts increased from $164,306 at
     December 31, 1999 to $239,771 at March 31, 2000. This increase was
     attributable to the delinquent account receivable balances of approximately
     12 lessees. The Leasing Company has either negotiated specific payment
     terms with these lessees or is pursuing other alternatives to collect the
     outstanding balances. In each instance, the Registrant believes it has
     provided sufficient reserves for all doubtful accounts.

     The Registrant's operating performance contributed to a 50% decline in net
     lease receivables at March 31, 2000 when compared to December 31, 1999. The
     Registrant's cash distribution from operations for the first quarter of
     2000 was 5.0% (annualized) of the limited partners' original capital
     contributions, unchanged from the fourth quarter of 1999. These
     distributions are directly related to the Registrant's results from
     operations and may fluctuate accordingly. The cash distribution from sales
     proceeds for the first quarter of 2000 was 0.25% (annualized) of the
     limited partners' original capital contribution, a decline from the 1.50%
     (annualized) in the fourth quarter of 1999. Sales proceeds to its partners
     may fluctuate in subsequent periods, reflecting the level of container
     disposals.

     In order to take advantage of improving market conditions and stronger
     demand for leased containers, the Registrant undertook a strategy that was
     aimed at significantly reducing its inventory of idle equipment in some
     low-demand locations while, at the same time, fulfilling lessee container
     requirements. As part of this strategy, the Registrant offered leasing
     incentives to several lessees for picking up off-hire equipment from the
     Registrant's higher inventory areas. This not only resulted in stronger
     utilization of the Registrant's equipment, but it also significantly
     lowered Partnership expenses related to storage and handling.


2)   Material changes in the results of operations between the three-month
     period ended March 31, 2000 and the three-month period ended March 31,
     1999.

     Net lease revenue for the three-month period ended March 31, 2000 was
     $954,521, a decline of 13% from the same period in the prior year. Gross
     rental revenue (a component of net lease revenue) for the three-month
     period ended March 31, 2000 was $1,759,088, reflecting a decline of 6% from
     the same period in the prior year. Gross lease revenue was primarily
     impacted by lower per-diem rental rates. Average dry cargo container
     per-diem rental rates for the three-month period ended March 31, 2000
     declined approximately 12%, when compared to the same period in the prior
     year. Average refrigerated container per-diem rental rates for the
     three-month period ended March 31, 2000 declined approximately 14%, when
     compared to the same period in the prior year.

                                       10

<PAGE>   11

     The Registrant's average fleet size and utilization rates for the
     three-month periods ended March 31, 2000 and 1999 were as follows:

<TABLE>
<CAPTION>

                                                    Three Months Ended
                                                 -------------------------
                                                 March 31,       March 31,
                                                    2000            1999
                                                 ---------       ---------

<S>                                              <C>             <C>
Average fleet size (measured in twenty-foot
   equivalent units (TEU))
      Dry cargo containers                          19,938          20,135
      Refrigerated containers                          775             807
Average utilization
      Dry cargo containers                              74%             66%
      Refrigerated containers                           84%             69%
</TABLE>



     Rental equipment operating expenses were 32% of the Registrant's gross
     lease revenue during the three-month period ended March 31, 2000, as
     compared to 29% during the three-month period ended March 31, 1999. The
     Registrant's operating results contributed to a 10% decline in base
     management fees when compared to the same period in the prior year.

     The Registrant disposed of 57 twenty-foot, 28 forty-foot and one forty-foot
     high-cube marine dry cargo containers, as well as one forty-foot
     refrigerated cargo container during the first quarter of 2000, compared to
     56 twenty-foot, 34 forty-foot and one forty-foot high-cube marine dry cargo
     containers during the same period in the prior year. The decision to repair
     or dispose of a container is made when it is returned by a lessee. This
     decision is influenced by various factors including the age, condition,
     suitability for continued leasing, as well as the geographical location of
     the container when disposed. These factors also influence the amount of
     sales proceeds received and the related gain or loss on container
     disposals.


     YEAR 2000

     The Registrant relies upon the financial and operational systems provided
     by the Leasing Company and its affiliates, as well as the systems provided
     by other independent third parties to service the three primary areas of
     its business: investor processing/maintenance; container leasing/asset
     tracking; and accounting/finance. Neither the Registrant nor the Leasing
     Company experienced nor do they currently anticipate any material adverse
     effects on the Registrant's business, results of operations or financial
     condition as a result of Year 2000 issues involving internal use systems,
     third party products or any of their software products. Costs incurred in
     preparing for Year 2000 issues were expensed as incurred. Neither the
     Registrant nor the Leasing Company anticipate any additional material costs
     in connection with Year 2000 uncertainties. Pursuant to the Limited
     Partnership Agreement, CCC or the Leasing Company, may not seek
     reimbursement of data processing costs associated with the Year 2000
     program.



Item 3. Quantitative and Qualitative Disclosures About Market Risk

        Not applicable.

                                       11

<PAGE>   12

                           PART II - OTHER INFORMATION


Item 6. Exhibits and Reports on Form 8-K



(a)  Exhibits

<TABLE>
<CAPTION>

  Exhibit
    No.                        Description                         Method of Filing
 ---------    -------------------------------------------------    --------------------
<S>           <C>                                                  <C>
   3(a)       Limited Partnership  Agreement of the Registrant,    *
              amended and restated as of December 2, 1991


   3(b)       Certificate of Limited Partnership of the            **
              Registrant


   10         Form of Leasing Agent Agreement with Cronos          ***
              Containers Limited


   27         Financial Data Schedule                              Filed with this document
</TABLE>

(b)  Reports on Form 8-K

     No reports on Form 8-K were filed by the Registrant during the quarter
ended March 31, 2000.


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

*     Incorporated by reference to Exhibit "A" to the Prospectus of the
      Registrant dated December 2, 1991, included as part of Registration
      Statement on Form S-1 (No. 33-42697)

**    Incorporated by reference to Exhibit 3.2 to the Registration Statement on
      Form S-1 (No. 33-42697)

***   Incorporated by reference to Exhibit 10.2 to the Registration Statement on
      Form S-1 (No. 33-42697)

                                       12


<PAGE>   13

                                   SIGNATURES



        Pursuant to the requirements 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.




                                    IEA INCOME FUND XII, L.P.


                                    By   Cronos Capital Corp.
                                         The General Partner




                                    By   /s/ Dennis J. Tietz
                                       -------------------------------------
                                         Dennis J. Tietz
                                         President and Director of Cronos
                                         Capital Corp. ("CCC")
                                         Principal Executive Officer of CCC




Date: May 15, 2000


                                       13

<PAGE>   14


                                  EXHIBIT INDEX

<TABLE>
<CAPTION>

  Exhibit
    No.                        Description                         Method of Filing
 ---------    -------------------------------------------------    --------------------
<S>           <C>                                                  <C>

   3(a)       Limited Partnership  Agreement of the Registrant,    *
              amended and restated as of December 2, 1991


   3(b)       Certificate of Limited Partnership of the            **
              Registrant


   10         Form of Leasing Agent Agreement with Cronos          ***
              Containers Limited


   27         Financial Data Schedule                              Filed with this document
</TABLE>


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

*     Incorporated by reference to Exhibit "A" to the Prospectus of the
      Registrant dated December 2, 1991, included as part of Registration
      Statement on Form S-1 (No. 33-42697)

**    Incorporated by reference to Exhibit 3.2 to the Registration Statement on
      Form S-1 (No. 33-42697)

***   Incorporated by reference to Exhibit 10.2 to the Registration Statement on
      Form S-1 (No. 33-42697)