<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 September 30, 1998

                                       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

                - September 30, 1998 and December 31, 1997                                         3

            Statements of Operations

                - Three month and nine month periods ended September 30, 1998 and 1997             4

            Statements of Cash Flows

                - Nine month periods ended September 30, 1998 and 1997                             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>
                                                                                         September 30,        December 31,
                                                                                             1998                 1997
                                                                                       ---------------      ---------------
                                                                                         (Unaudited)
         <S>                                                                          <C>                  <C>            
         ASSETS:

         Current Assets:
              Cash and cash equivalents                                                $        1,633       $        1,173 
              Oil and gas sales receivable                                                    165,093              436,486 
              Other                                                                             9,441                6,468 
                                                                                       ---------------      ---------------
                  Total Current Assets                                                        176,167              444,127 
                                                                                       ---------------      ---------------

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

         Oil and Gas Properties, using full cost
              accounting                                                                   12,809,959           12,752,686 
         Less-Accumulated depreciation, depletion
              and amortization                                                            (11,252,160)         (10,677,142)
                                                                                       ---------------      ---------------
                                                                                            1,557,799            2,075,544 
                                                                                       ---------------      ---------------
                                                                                       $    1,734,312       $    2,519,671 
                                                                                       ===============      ===============

         LIABILITIES AND PARTNERS' CAPITAL:

         Current Liabilities:
             Accounts Payable                                                          $       38,384       $       88,549 
                                                                                       ---------------      ---------------

         Deferred Revenues                                                                    105,572              125,660 

         Limited Partners' Capital (14,121.10 Limited Partnership Units;
                                   $1,000 per unit)                                         1,505,486            2,195,259 
         General Partners' Capital                                                             84,870              110,203 
                                                                                       ---------------     ----------------
                  Total Partners' Capital                                                   1,590,356            2,305,462 
                                                                                       ---------------      ---------------
                                                                                       $    1,734,312       $    2,519,671 
                                                                                       ===============      ===============
</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                    Nine Months Ended
                                                       September 30,                        September 30,
                                              ---------------------------------  ---------------------------------
                                                   1998              1997               1998             1997
                                              ----------------   --------------  ---------------   ---------------
<S>                                           <C>               <C>              <C>               <C>             
REVENUES:
   Oil and gas sales                          $        65,705   $        89,810  $       199,083   $       350,088 
   Interest income                                      1,051               579            5,186             1,682 
   Other                                                  306               903              849             3,497 
                                              ---------------   ---------------  ---------------   --------------- 
                                                       67,062            91,292          205,118           355,267 
                                              ---------------   ---------------  ---------------   --------------- 

COSTS AND EXPENSES:
   Lease operating                                     15,056            44,254           92,253           146,133 
   Production taxes                                     2,792             5,244            9,396            16,830 
   Depreciation, depletion
      and amortization -
        Normal                                         39,062            25,835          108,051           100,040 
        Additional                                    466,967                --          466,967                -- 
   General and administrative                           4,344            11,753           67,917            74,600 
                                              ---------------   ---------------  ---------------   --------------- 
                                                      528,221            87,086          744,584           337,603 
                                              ---------------   ---------------  ---------------   --------------- 
NET INCOME (LOSS)                             $      (461,159)  $         4,206  $      (539,466)  $        17,644 
                                              ===============   ===============  ===============   ===============



Limited Partners' net income (loss)
   per unit                                   $        (32.66)  $           .30  $        (38.20)  $          1.25 
                                              ===============   ===============  ===============   ===============
</TABLE>


                 See accompanying notes to financial statements.

                                        4


<PAGE>

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

<TABLE>
<CAPTION>
                                                                                           Nine Months Ended
                                                                                             September 30,
                                                                               ---------------------------------------- 
                                                                                     1998                     1997
                                                                               ---------------          --------------- 
<S>                                                                             <C>                     <C>             
CASH FLOWS FROM OPERATING ACTIVITIES:
    Income (Loss)                                                               $     (539,466)         $        17,664 
    Adjustments to reconcile income (loss) to
      net cash provided by operations:
      Depreciation, depletion and amortization                                         575,018                  100,040 
      Change in gas imbalance receivable
         and deferred revenues                                                         (20,434)                  (2,361)
      Change in assets and liabilities:
        (Increase) decrease in oil and gas sales receivable                            271,393                   74,954 
        (Increase) decrease in other current assets                                     (2,973)                  (5,077)
        Increase (decrease) in accounts payable                                        (50,165)                 (49,819)
                                                                               ---------------          --------------- 
               Net cash provided by (used in) operating activities                     233,373                  135,401 
                                                                               ---------------          --------------- 
CASH FLOWS FROM INVESTING ACTIVITIES:
    Additions to oil and gas properties                                                (57,273)                 (14,743)
    Proceeds from sales of oil and gas properties                                           --                    2,101 
    (Increase) decrease in receivable due to property disposition                           --                  105,380 
                                                                               ---------------          --------------- 
               Net cash provided by (used in) investing activities                     (57,273)                  92,738 
                                                                               ---------------          --------------- 
CASH FLOWS FROM FINANCING ACTIVITIES:
    Cash distributions to partners                                                    (175,640)                (228,021)
                                                                               ---------------          --------------- 
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                                       460                      118 
                                                                               ---------------          --------------- 
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                                         1,173                    1,029 
                                                                               ---------------          --------------- 

CASH AND CASH EQUIVALENTS AT END OF PERIOD                                      $        1,633          $         1,147 
                                                                               ===============          =============== 
</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,  1997  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  gas  imbalance   receivable  and  deferred  revenues  are
        accounted  for on  the  entitlements  method,  whereby  the  Partnership
        records its share of revenue,  based on its entitled amount. Any amounts
        over or under  the  entitled  amount  are  recorded  as an  increase  or
        decrease  to the  gas  imbalance  receivable  or  deferred  revenues  as
        applicable.

(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 year  1900 and 2000.  The  Managing  General  Partner  is  currently
        implementing  the steps necessary to make its operations and the related
        operations of the Partnership  Year 2000 compliant.  These steps include
        upgrading,  testing and certifying  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 the year to address the Year 2000 issue to ensure that all
        of its business systems are Year 2000 compliant by mid-1999 with mission
        critical systems projected to be compliant by the end of 1998.

                  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 will be conducted as the software is updated or certified
        and is expected to be complete by mid-1999.


                                       6
<PAGE>

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


                  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,  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 in the next nine months.  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 a 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.  The
        Managing  General Partner is uncertain,  however,  as to the impact that
        the Year  2000  issue  will  have on field  operations  or as to how the
        Managing General Partner or the Partnership will be indirectly  affected
        by the impact that the Year 2000 issue will have on companies with which
        it conducts  business.  For example,  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  plans  to  contact  its  major   purchasers,
        customers,  suppliers,  financial  institutions  and others with whom it
        conducts  business to determine whether they will be Year 2000 compliant
        and  whether  they will be able to resolve  in a timely  manner any Year
        2000  problems.  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  $233,373  and $135,401 for the nine
months ended September 30, 1998 and 1997, 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  $175,640 and $228,021 for the nine months ended  September 30, 1998 and
1997, respectively.

      The  Partnership  does  not  allow  for  additional  assessments  from the
partners  to fund  capital  requirements.  However,  funds  in  addition  to the
remaining  unexpended net capital commitments of the partners are available from
partnership  revenues,  borrowings  or  proceeds  from the  sale of  partnership
property.  The  Managing  General  Partner  believes  that the  funds  currently
available to the Partnership  will be adequate to meet any  anticipated  capital
requirements.

RESULTS OF OPERATIONS

      The  following  analysis  explains  changes  in the  revenue  and  expense
categories  for the quarter  ended  September  30, 1998  (current  quarter) when
compared to the quarter ended September 30, 1997  (corresponding  quarter),  and
for the nine months ended September 30, 1998 (current period),  when compared to
the nine months ended September 30, 1997 (corresponding period).

Three Months Ended September 30, 1998 and 1997

      Oil and gas sales  declined  $24,105 or 27 percent in the third quarter of
1998 when  compared  to the  corresponding  quarter  in 1997,  primarily  due to
decreased gas and oil prices.  A decline in gas prices of 23 percent or $.56/MCF
and in oil  prices  of 34  percent  or  $5.80/BBL  had a  significant  impact on
partnership  performance.  Also,  current  quarter  oil  production  declined 47
percent when  compared to third  quarter 1997 oil  production  volumes,  further
contributing to decreased revenues. The partnership's sale of several properties
in the  fourth  quarter  of 1997 had an  impact on 1998  partnership  production
volumes.  Corresponding  operating  expenses  declined  66  percent in the third
quarter of 1998 when compared to the third quarter of 1997.

      Associated  depreciation  expense  increased 51 percent or $13,227 in 1998
compared to third quarter 1997.


                                       8


<PAGE>


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


      The  Partnership   recorded  an  additional   provision  in  depreciation,
depletion  and  amortization  in the third quarter of 1998 for $466,967 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,  was below the fair  market  value  originally  paid for oil and gas
properties. The additional provision results from the Managing General Partner's
determination  that the fair  market  value paid for  properties  may or may not
coincide  with reserve  valuations  determined  according to  guidelines  of the
Securities and Exchange Commission.

Nine Months Ended September 30, 1998 and 1997

      Oil and gas sales declined $151,005 or 43 percent in the first nine months
of 1998 when  compared to the  corresponding  period in 1997,  primarily  due to
decreased gas and oil prices.  A decline in gas prices of 25 percent or $.59/MCF
and in oil  prices  of 36  percent  or  $6.44/BBL  had a  significant  impact on
partnership performance. Also, current period oil and gas production declined 55
percent and 12 percent, respectively,  when compared to the same period in 1997,
further  contributing to decreased  revenues.  The partnership's sale of several
properties  in the  fourth  quarter  of 1997 had an impact  on 1998  partnership
production volumes. Corresponding operting expenses for the first nine months of
1998 decreased 37 percent when compared to the same period in 1997.

      Associated  depreciation  expense  increased  8 percent  or $8,011 in 1998
compared to the first nine months of 1997.

      The  Partnership   recorded  an  additional   provision  in  depreciation,
depletion  and  amortization  in the first nine months of 1998 for $466,967 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,  was below the fair  market  value  originally  paid for oil and gas
properties. The additional provision results from the Managing General Partner's
determination  that the fair  market  value paid for  properties  may or may not
coincide  with reserve  valuations  determined  according to  guidelines  of the
Securities and Exchange Commission.

      During 1998,  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:  November 4, 1998              By:        /s/ John R. Alden
       ----------------                         --------------------------------
                                                John R. Alden
                                                Senior Vice President, Secretary
                                                and Principal Financial Officer

Date:  November 4, 1998              By:        /s/ Alton D. Heckaman, Jr.
       ----------------                         --------------------------------
                                                Alton D. Heckaman, Jr.
                                                Vice President, Controller
                                                and Principal Accounting Officer


                                       11