<PAGE>

                                    FORM 10-Q



                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549


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

                  For the quarterly period ended March 31, 1999

                                       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 0-17023


                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
             (Exact name of registrant as specified in its charter)

<TABLE>
<S>                                           <C>
                  Texas                                   76-0208087
(State or other jurisdiction of organization) (I.R.S. Employer Identification No.)
</TABLE>


                        16825 Northchase Drive, Suite 400
                              Houston, Texas 77060
                    (Address of principal executive offices)
                                   (Zip Code)

                                  (281)874-2700
              (Registrant's telephone number, including area code)

                                      None
              (Former name, former address and former fiscal year,
                          if changed since last report)


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>

                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.

                                      INDEX



<TABLE>
<CAPTION>
PART I.    FINANCIAL INFORMATION                                     PAGE
      <S>                                                              <C>
      ITEM 1.    Financial Statements

            Balance Sheets

                - March 31, 1999 and December 31, 1998                 3

            Statements of Operations

                - Three month periods ended March 31, 1999 and 1998    4

            Statements of Cash Flows

                - Three month periods ended March 31, 1999 and 1998    5

            Notes to Financial Statements                              6

      ITEM 2.    Management's Discussion and Analysis of Financial
                     Condition and Results of Operations               8

PART II.    OTHER INFORMATION                                         10


SIGNATURES                                                            11
</TABLE>


<PAGE>


                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                                 BALANCE SHEETS


<TABLE>
<CAPTION>
                                                                                           March 31,         December 31,
                                                                                             1999                 19987
                                                                                       ---------------      ---------------
                                                                                         (Unaudited)
         <S>                                                                           <C>                  <C>           
         ASSETS:

         Current Assets:
              Cash and cash equivalents                                                $        1,676       $        1,669 
              Oil and gas sales receivable                                                    138,195              163,057 
              Other                                                                            12,845               10,882 
                                                                                       ---------------      ---------------
                  Total Current Assets                                                        152,716              175,608 
                                                                                       ---------------      ---------------

         Gas Imbalance Receivable                                                                 346                  346 
                                                                                       ---------------      ---------------

         Oil and Gas Properties, using full cost
              accounting                                                                   12,814,678           12,812,427 
         Less-Accumulated depreciation, depletion
              and amortization                                                            (11,326,395)         (11,298,612)
                                                                                       ---------------      ---------------
                                                                                            1,488,283            1,513,815 
                                                                                       ---------------      ---------------
                                                                                       $    1,641,345       $    1,689,769 
                                                                                       ===============      ===============

         LIABILITIES AND PARTNERS' CAPITAL:

         Current Liabilities:
             Accounts Payable                                                          $       43,673       $       30,979 
                                                                                       ---------------      ---------------

         Deferred Revenues                                                                    104,574              104,574 

         Limited Partners' Capital (14,121.10 Limited Partnership Units;
                                   $1,000 per unit)                                         1,419,857            1,475,276 
         General Partners' Capital                                                             73,241               78,940 
                                                                                       ---------------      ---------------
                  Total Partners' Capital                                                   1,493,098            1,554,216 
                                                                                       ---------------      ---------------
                                                                                       $    1,641,345       $    1,689,769 
                                                                                       ===============      ===============
</TABLE>


                 See accompanying notes to financial statements.

                                        3


<PAGE>

                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                            STATEMENTS OF OPERATIONS
                                   (Unaudited)


<TABLE>
<CAPTION>
                                                                                         Three Months Ended
                                                                                              March 31,
                                                                                 ---------------------------------
                                                                                      1999                   1998
                                                                                 ---------------   ---------------
         <S>                                                                     <C>               <C>
         REVENUES:
             Oil and gas sales                                                   $        40,651   $        40,575 
             Interest income                                                               1,970             2,337 
             Other                                                                            --               229 
                                                                                 ---------------   --------------- 
                                                                                          42,621            43,141 
                                                                                 ---------------   --------------- 
         COSTS AND EXPENSES:
             Lease operating                                                              14,634            44,546 
             Production taxes                                                              2,039             2,611 
             Depreciation, depletion
               and amortization                                                           27,783            24,085 
             General and administrative                                                   29,715            37,832 
                                                                                 ---------------   --------------- 
                                                                                          74,171           109,074 
                                                                                 ---------------   --------------- 
         NET INCOME (LOSS)                                                       $       (31,550)  $       (65,933)
                                                                                 ===============   =============== 

</TABLE>

         Limited Partners' net income (loss)
             per unit

         March 31, 1999                       $         (2.18)
                                                 ============ 
         March 31, 1998                       $         (4.67)
                                                 ============ 


                 See accompanying note to financial statements.

                                        4


<PAGE>

                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                            STATEMENTS OF CASH FLOWS
                                   (Unaudited)

<TABLE>
<CAPTION>
                                                                                           Three Months Ended
                                                                                                March 31,
                                                                               ----------------------------------------
                                                                                     1999                    1998
                                                                               ---------------          ---------------
<S>                                                                             <C>                     <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
    Income (loss)                                                               $      (31,550)         $       (65,933)
    Adjustments to reconcile income (loss) to
      net cash provided by operations:
      Depreciation, depletion and amortization                                          27,783                   24,085 
      Change in gas imbalance receivable
          and deferred revenues                                                             --                     (346)
      Change in assets and liabilities:
        (Increase) decrease in oil and gas sales receivable                             24,862                  223,309 
        (Increase) decrease in other current assets                                     (1,963)                  (2,331)
        Increase (decrease) in accounts payable                                         12,694                   12,730 
                                                                               ---------------          --------------- 
                Net cash provided by (used in) operating activities                     31,826                  191,514 
                                                                               ---------------          --------------- 
CASH FLOWS FROM INVESTING ACTIVITIES:
    Additions to oil and gas properties                                                 (2,251)                  (9,481)
                                                                               ---------------          --------------- 
CASH FLOWS FROM FINANCING ACTIVITIES:
    Cash distributions to partners                                                     (29,568)                 (80,149)
                                                                               ---------------          --------------- 
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                                         7                  101,884 
                                                                               ---------------          --------------- 
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                                         1,669                    1,173 
                                                                               ---------------          --------------- 
CASH AND CASH EQUIVALENTS AT END OF PERIOD                                      $        1,676          $       103,057 
                                                                               ===============          =============== 
</TABLE>


                 See accompanying notes to financial statements.

                                        5


<PAGE>

                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                          NOTES TO FINANCIAL STATEMENTS
                                   (UNAUDITED)


(1)  General Information -

                  The financial statements included herein have been prepared by
        the  Partnership  and are  unaudited  except  for the  balance  sheet at
        December  31,  1998  which has been  taken  from the  audited  financial
        statements at that date. The financial  statements reflect  adjustments,
        all of which  were of a  normal  recurring  nature,  which  are,  in the
        opinion  of  the  managing   general   partner   necessary  for  a  fair
        presentation.  Certain  information  and footnote  disclosures  normally
        included in financial  statements  prepared in accordance with generally
        accepted  accounting  principles have been omitted pursuant to the rules
        and regulations of the Securities and Exchange Commission  ("SEC").  The
        Partnership  believes adequate disclosure is provided by the information
        presented.  The financial  statements should be read in conjunction with
        the audited  financial  statements  and the notes included in the latest
        Form 10-K.

(2)  Gas Imbalances -

                  The Partnership  recognizes its ownership  interest in natural
        gas  production as revenue.  Actual  production  quantities  sold may be
        different than the  Partnership's  ownership share in a given period. If
        the  Partnership's  sales exceed its ownership share of production,  the
        differences are recorded as deferred revenue. Gas balancing  receivables
        are  recorded  when the  Partnership's  ownership  share  of  production
        exceeds sales.

(3)  Vulnerability Due to Certain Concentrations -

                  The  Partnership's  revenues are primarily the result of sales
        of its oil and natural gas production.  Market prices of oil and natural
        gas may fluctuate and adversely affect operating results.

                  In the normal  course of  business,  the  Partnership  extends
        credit,  primarily in the form of monthly oil and gas sales receivables,
        to various  companies  in the oil and gas  industry  which  results in a
        concentration  of credit risk. This  concentration of credit risk may be
        affected by changes in economic or other  conditions and may accordingly
        impact the  Partnership's  overall  credit risk.  However,  the Managing
        General  Partner  believes  that  the  risk is  mitigated  by the  size,
        reputation, and nature of the companies to which the Partnership extends
        credit.  In  addition,   the  Partnership  generally  does  not  require
        collateral or other security to support customer receivables.

(4)  Fair Value of Financial Instruments -

                  The Partnership's  financial  instruments  consist of cash and
        cash equivalents and short-term  receivables and payables.  The carrying
        amounts  approximate  fair value due to the highly  liquid nature of the
        short-term instruments.

(5)  Year 2000 -

                  The  Year  2000  issue  results  from  computer  programs  and
        embedded computer chips with date fields that cannot distinguish between
        the years 1900 and 2000.  The  Managing  General  Partner  is  currently
        implementing  the steps necessary to make its operations and the related
        operations of the Partnership capable of addressing the Year 2000. These
        steps include upgrading, testing and certifying its computer systems and
        field   operation   services   and   obtaining   Year  2000   compliance
        certification  from  all  important  business  suppliers.  The  Managing
        General Partner formed a task force during 1998 to address the Year 2000
        issue and prepare its business  systems for the Year 2000.  By mid-1999,
        the Managing  General Partner expects the mission critical systems to be
        either replaced or updated and testing to be virtually completed.


                                       6

<PAGE>


                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                    NOTES TO FINANCIAL STATEMENTS (CONTINUED)
                                   (UNAUDITED)


                  The Managing  General  Partner's  business  systems are almost
        entirely  comprised of  off-the-shelf  software.  Most of the  necessary
        changes in computer  instructional  code can be made by  upgrading  this
        software.  The Managing  General  Partner is currently in the process of
        either upgrading the off-the-shelf  software or receiving  certification
        as to Year 2000  compliance from vendors or third party  consultants.  A
        testing phase is being conducted as the software is updated or certified
        and is expected to be completed by mid-1999.

                  The  Managing  General  Partner  does not  believe  that costs
        incurred  to address  the Year 2000 issue with  respect to its  business
        systems  will have a  material  effect on the  Partnership's  results of
        operations,  or its  liquidity and  financial  condition.  The estimated
        total cost to the Managing  General  Partner to address Year 2000 issues
        is  projected  to be less  than  $150,000,  most of which  will be spent
        during  the  testing  phase.  The  Partnership's  share of this  cost is
        expected to be insignificant.

                  The  failure  to correct a material  Year 2000  problem  could
        result  in an  interruption,  or  failure  of  certain  normal  business
        activities or  operations.  Based on  activities  to date,  the Managing
        General  Partner  believes that it will be able to resolve any Year 2000
        problems  concerning  its financial and  administrative  systems.  It is
        undeterminable  how all the  aspects  of the Year 2000 will  impact  the
        Partnership.  The most  reasonably  likely  worst  case  scenario  would
        involve a prolonged disruption of external power sources upon which core
        equipment   relies,   resulting  in  a   substantial   decrease  in  the
        Partnership's  oil and  gas  production  activities.  In  addition,  the
        pipeline  operators  to whom the  Managing  General  Partner  sells  the
        Partnership's  natural gas, as well as other  customers  and  suppliers,
        could be prone to Year  2000  problems  that  could not be  assessed  or
        detected by the Managing General  Partner.  The Managing General Partner
        is contacting  its major  purchasers,  customers,  suppliers,  financial
        institutions  and others  with whom it conducts  business  to  determine
        whether  they will be able to resolve  in a timely  manner any Year 2000
        problems directly  affecting the Managing General Partner or Partnership
        and to inform them of the Managing General Partner's internal assessment
        of its Year 2000  review.  There  can be no  assurance  that such  third
        parties will not fail to appropriately address their Year 2000 issues or
        will not  themselves  suffer a Year 2000  disruption  that  could have a
        material  adverse  effect  on the  Partnership's  activities,  financial
        condition  or  operating  results.  Based upon these  responses  and any
        problems  that arise  during the  testing  phase,  contingency  plans or
        back-up systems would be determined and addressed.

                                       7


<PAGE>

                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL
                       CONDITION AND RESULTS OF OPERATIONS


General

         The  Partnership  was formed for the purpose of  investing in producing
oil and gas properties located within the continental United States. In order to
accomplish  this,  the  Partnership  goes through two  distinct yet  overlapping
phases  with  respect  to its  liquidity  and  results of  operations.  When the
Partnership  is formed,  it commences its  "acquisition"  phase,  with all funds
placed in short-term  investments until required for such property acquisitions.
The interest  earned on these  pre-acquisition  investments  becomes the primary
cash flow source for initial partner distributions.  As the Partnership acquires
producing   properties,   net  cash  from  operations   becomes   available  for
distribution,  along with the investment  income.  After  partnership funds have
been expended on producing oil and gas properties,  the  Partnership  enters its
"operations" phase. During this phase, oil and gas sales generate  substantially
all revenues,  and  distributions  to partners  reflect those  revenues less all
associated  partnership expenses.  The Partnership may also derive proceeds from
the sale of acquired oil and gas properties, when the sale of such properties is
economically appropriate or preferable to continued operation.

Liquidity and Capital Resources

      Oil and gas reserves are depleting  assets and therefore often  experience
significant  production  declines each year from the date of acquisition through
the end of the life of the  property.  The primary  source of  liquidity  to the
Partnership comes almost entirely from the income generated from the sale of oil
and gas produced from ownership  interests in oil and gas  properties.  Net cash
provided by  operating  activities  totaled  $31,826 and  $191,514 for the three
months ended March 31, 1999 and 1998, respectively. This source of liquidity and
the related results of operations, and in turn cash distributions,  will decline
in  future  periods  as the oil and gas  produced  from  these  properties  also
declines while production and general and administrative costs remain relatively
stable making it unlikely that the  Partnership  will hold the properties  until
they are fully depleted,  but will likely liquidate when a substantial  majority
of the reserves  have been  produced.  The  Partnership  has expended all of the
partners' net commitments available for property acquisitions and development by
acquiring producing oil and gas properties. The partnership invests primarily in
proved  producing  properties with nominal levels of future costs of development
for  proven  but  undeveloped  reserves.  Significant  purchases  of  additional
reserves or extensive drilling activity are not anticipated.  Cash distributions
totaled  $29,568 and $80,149 for the three months ended March 31, 1999 and 1998,
respectively.

      The  Partnership  does  not  allow  for  additional  assessments  from the
partners to fund capital requirements.  The Managing General Partner anticipates
that the  Partnership  will have adequate  liquidity from income from continuing
operations  to  satisfy  any  future  capital  expenditure  requirements.  Funds
generated  from  bank  borrowings  and  proceeds  from  the  sale of oil and gas
properties will be used to supplement this effort if deemed necessary.

Results of Operations

      Oil and gas sales were flat in the first  quarter of 1999 when compared to
the  corresponding  quarter in 1998 as an increase in oil  production  and price
offset a small  decrease  in gas  production.  Gas  prices  remained  steady  at
$1.56/MCF  while  oil  prices  increased  19  percent  or  $1.84  to an  average
$11.47/BBL for the quarter.

      Corresponding  production costs per equivalent MCF decreased 65 percent in
the first quarter of 1999 as total  production  costs  decreased 65 percent when
compared to the first quarter of 1998, during which the Partnership performed an
expense workover on two wells in Texas.

      Associated  depreciation  expense  increased  15 percent or $3,698 in 1999
compared  to first  quarter  1998,  related to the  increase  in oil  production
volumes.


                                       8

<PAGE>


                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL
                 CONDITION AND RESULTS OF OPERATIONS (CONTINUED)


      The Partnership records an additional provision in depreciation, depletion
and amortization when the present value, discounted at ten percent, of estimated
future net revenues  from oil and gas  properties,  using the  guidelines of the
Securities and Exchange  Commission,  is below the fair market value  originally
paid for oil and gas  properties.  Using prices in effect at March 31, 1999, the
Partnership would have recorded an additional provision at March 31, 1999 in the
amount of $32,640.  However,  these temporarily low quarter-end prices rebounded
and by using prices in effect at the filing date, the Partnership's  unamortized
cost of oil and gas properties were not limited by this calculation.

      During 1999,  partnership  revenues  and costs will be shared  between the
limited partners and general partners in a 90:10 ratio.


                                       9


<PAGE>

                    SWIFT ENERGY INCOME PARTNERS 1986-D, LTD.
                           PART II - OTHER INFORMATION




ITEM 5.    OTHER INFORMATION


                                     -NONE-


                                       10


<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.


                                                SWIFT ENERGY INCOME
                                                PARTNERS 1986-D, LTD.
                                                (Registrant)

                                     By:        SWIFT ENERGY COMPANY
                                                Managing General Partner


Date:     May 5, 1999                By:        /s/ John R. Alden
          -----------                           --------------------------------
                                                John R. Alden
                                                Senior Vice President, Secretary
                                                and Principal Financial Officer

Date:     May 5, 1999                By:        /s/ Alton D. Heckaman, Jr.
          -----------                           --------------------------------
                                                Alton D. Heckaman, Jr.
                                                Vice President, Controller
                                                and Principal Accounting Officer


                                        11