<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, 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

                - September 30, 1999 and December 31, 1998                                         3

            Statements of Operations

                - Three month and nine month periods ended September 30, 1999 and 1998             4

            Statements of Cash Flows

                - Nine month periods ended September 30, 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>
                                                                                 September 30,        December 31,
                                                                                    1999                 1998
                                                                               ---------------       ---------------
                                                                                 (Unaudited)
<S>                                                                          <C>                   <C>
ASSETS:

Current Assets:
     Cash and cash equivalents                                               $          1,715      $          1,669
     Oil and gas sales receivable                                                     142,233               163,057
     Other                                                                             14,423                10,882
                                                                               ---------------       ---------------
          Total Current Assets                                                        158,371               175,608
                                                                               ---------------       ---------------

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

Oil and Gas Properties, using full cost
     accounting                                                                    12,819,062            12,812,427
Less-Accumulated depreciation, depletion
     and amortization                                                            (11,392,847)          (11,298,612)
                                                                               ---------------       ---------------
                                                                                    1,426,215             1,513,815
                                                                               ===============       ===============
                                                                             $      1,584,932      $      1,689,769
                                                                               ===============       ===============


LIABILITIES AND PARTNERS' CAPITAL:

Current Liabilities:
     Accounts Payable                                                        $         32,960      $         30,979
                                                                               ---------------       ---------------

Deferred Revenues                                                                      92,110               104,574

Limited Partners' Capital (14,121.10 Limited Partnership
                          Units; $1,000 per unit)                                   1,380,688             1,475,276

General Partners' Capital                                                              79,174                78,940
                                                                               ---------------       ---------------
          Total Partners' Capital                                                   1,459,862             1,554,216
                                                                               ===============       ===============
                                                                             $      1,584,932      $      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                       Nine Months Ended
                                                       September 30,                           September 30,
                                             ---------------------------------        ---------------------------------
                                                   1999              1998                  1999              1998
                                             --------------     --------------        --------------     --------------
<S>                                       <C>                 <C>                  <C>                <C>
REVENUES:
     Oil and gas sales                    $         88,509    $        65,705      $        184,906   $        199,083
     Interest income                                 1,259              1,051                 3,587              5,186
     Other                                              --                306                    --                849
                                             --------------     --------------        --------------     --------------
                                                    89,768             67,062               188,493            205,118
                                             --------------     --------------        --------------     --------------


COSTS AND EXPENSES:
     Lease operating                                17,596             15,056                51,052             92,253
     Production taxes                                4,475              2,792                 9,909              9,396
     Depreciation, depletion
          and amortization -
             Normal                                 39,549             39,062                94,235            108,051
             Additional                                 --            466,967                    --            466,967
     General and administrative                      6,149              4,344                58,660             67,917
                                             --------------     --------------        --------------     --------------
                                                    67,769            528,221               213,856            744,584
                                             ==============     ==============        ==============     ==============
NET INCOME (LOSS)                         $         21,999    $      (461,159)     $        (25,363)  $       (539,466)
                                             ==============     ==============        ==============     ==============




Limited Partners' net income (loss)
     per unit                             $           1.16    $        (32.66)     $          (2.19)  $         (38.20)
                                             ==============     ==============        ==============     ==============
</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,
                                                                                   -------------------------------------
                                                                                        1999                  1998
                                                                                   ---------------       ---------------
<S>                                                                              <C>                   <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
     Income (loss)                                                               $       (25,363)      $       (539,466)
     Adjustments to reconcile income (loss) to
          net cash provided by operations:
          Depreciation, depletion and amortization                                        94,235                575,018
          Change in gas imbalance receivable
               and deferred revenues                                                     (12,464)               (20,434)
          Change in assets and liabilities:
               (Increase) decrease in oil and gas sales receivable                        20,824                271,393
               (Increase) decrease in other current assets                                (3,541)                (2,973)
               Increase (decrease) in accounts payable                                     1,981                (50,165)
                                                                                   ---------------       ---------------
          Net cash provided by (used in) operating activities                             75,672                233,373
                                                                                   ---------------       ---------------

CASH FLOWS FROM INVESTING ACTIVITIES:
     Additions to oil and gas properties                                                  (6,635)               (57,273)
                                                                                   ---------------       ---------------

CASH FLOWS FROM FINANCING ACTIVITIES:
     Cash Distributions to partners                                                      (68,991)              (175,640)
                                                                                   ---------------       ---------------
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                                          46                    460
                                                                                   ---------------       ---------------
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                                           1,669                  1,173
                                                                                   ===============       ===============
CASH AND CASH EQUIVALENTS AT END OF PERIOD                                       $         1,715       $          1,633
                                                                                   ===============       ===============
</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 has  implemented
        the steps necessary to make its operations and the related operations of
        the  Partnership  capable  of  addressing  the Year  2000.  These  steps
        included  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.  The Managing
        General Partner has either replaced or updated mission  critical systems
        and has  substantially  completed  testing  and will  continue  remedial
        actions as needed.

                  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 were made by  upgrading  this
        software.  In  addition,  the  Managing  General  Partner  has  received
        certification  as to Year 2000  compliance  from  vendors or third party
        consultants.

                                       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,  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 was 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 has resolved 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
        has  contacted 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,  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. 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.  Cash distributions to
partners are determined quarterly,  based upon net proceeds from sale of oil and
gas production after payment of lease operating  expense,  taxes and development
costs, less general and administrative expenses. In addition, future partnership
cash requirements are taken into account to determine necessary cash reserves.

      Net cash provided by operating activities totaled $75,672 and $233,373 for
the nine months ended September 30, 1999 and 1998,  respectively.  In 1999, cash
provided  by  operating  activities  and cash  distributions  were  effected  by
production declines from the Partnership's  depleting property  interests.  Cash
distributions  totaled  $68,991 and $175,640 for the nine months ended September
30, 1999 and 1998, respectively. Cash distributions in 1999 were effected by low
oil and gas prices received during the first part of this year.

      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.  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, 1999  (current  quarter) when
compared to the quarter ended September 30, 1998  (corresponding  quarter),  and
for the nine months ended September 30, 1999 (current period),  when compared to
the nine months ended September 30, 1998 (corresponding period).

Three Months Ended September 30, 1999 and 1998

       Oil and gas sales increased $22,804 or 35 percent in the third quarter of
1999 when  compared  to the  corresponding  quarter  in 1998,  primarily  due to
increased oil and gas prices. Oil prices increased 65 percent or $7.23/BBL to an
average of  $18.39/BBL  and gas prices  increased  31 percent or  $.57/MCF to an
average of $2.40/MCF  for the quarter.  Increased  oil prices  helped offset the
effect of decreased oil production.  Current quarter production volumes remained
flat as oil  production  declined  36 percent  and gas  production  increased  8
percent when compared to third quarter 1998 production volumes.

                                       8


<PAGE>


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


      Corresponding  production costs per equivalent MCF increased 22 percent in
the  third  quarter  of 1999  compared  to the third  quarter  of 1998 and total
production costs increased 24 percent.

      Total  depreciation  expense for the third  quarter of 1999  decreased  92
percent or $466,480 when  compared to the third  quarter of 1998.  In 1998,  two
components, the normal provision,  calculated on the units of production method,
and the additional provision,  relating to the ceiling limitation, make up total
depreciation  expense.  Normal  depreciation  expense remained flat in the third
quarter of 1999 compared to the third quarter of 1998.

      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.

Nine Months Ended September 30, 1999 and 1998

      Oil and gas sales  declined  $14,177 or 7 percent in the first nine months
of 1999 when  compared to the  corresponding  period in 1998,  primarily  due to
decreased oil and gas production. Current period production volumes decreased 21
percent  as  oil  and  gas  production  declined  27  percent  and  21  percent,
respectively,  when compared to the same period in 1998. Production declines are
a result of the accelerated  depletion of the  Partnership's  mature wells.  Oil
prices  increased 31 percent or $3.53/BBL  to an average of  $14.93/BBL  and gas
prices  increased  17 percent or  $.30/MCF  to an average of  $2.12/MCF  for the
current  period.  Increased  oil and gas  prices  helped  offset  the  effect of
decreased production.

      Corresponding  production costs per equivalent MCF decreased 23 percent in
the first nine months of 1999 compared to the  corresponding  period in 1998 and
total production costs decreased 40 percent.

      Total depreciation  expense for the first nine months of 1999 decreased 84
percent or $480,783 when compared to the first nine months of 1998. In 1998, two
components, the normal provision,  calculated on the units of production method,
and the additional provision,  relating to the ceiling limitation, make up total
depreciation  expense.  Normal  depreciation  expense  decreased  13  percent or
$13,816 in the first nine  months of 1999  compared  to the first nine months of
1998.

      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.

      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:  November 4, 1999              By:        /s/ John R. Alden
       ----------------                         --------------------------------
                                                John R. Alden
                                                Senior Vice President, Secretary
                                                and Principal Financial Officer

Date:  November 4, 1999              By:        /s/ Alton D. Heckaman, Jr.
       ----------------                         --------------------------------
                                                Alton D. Heckaman, Jr.
                                                Vice President, Controller
                                                and Principal Accounting Officer


                                       11