<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 June 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

                - June 30, 1999 and December 31, 1998                                  3

            Statements of Operations

                - Three month and six month periods ended June 30, 1999 and 1998       4

            Statements of Cash Flows

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

Current Assets:
     Cash and cash equivalents                                               $          1,695      $          1,669
     Oil and gas sales receivable                                                     125,405               163,057
     Other                                                                             13,184                10,882
                                                                               ---------------       ---------------
          Total Current Assets                                                        140,284               175,608
                                                                               ---------------       ---------------

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

Oil and Gas Properties, using full cost
     accounting                                                                    12,818,062            12,812,427
Less-Accumulated depreciation, depletion
     and amortization                                                             (11,353,298)          (11,298,612)
                                                                               ---------------       ---------------
                                                                                    1,464,764             1,513,815
                                                                               ===============       ===============
                                                                             $      1,605,394      $      1,689,769
                                                                               ===============       ===============


LIABILITIES AND PARTNERS' CAPITAL:

Current Liabilities:
     Accounts Payable                                                        $         41,233      $         30,979
                                                                               ---------------       ---------------

Deferred Revenues                                                                     104,574               104,574

Limited Partners' Capital (14,121.10 Limited Partnership
                          Units; $1,000 per unit)                                   1,385,537             1,475,276
General Partners' Capital                                                              74,050                78,940
                                                                               ---------------       ---------------
          Total Partners' Capital                                                   1,459,587             1,554,216
                                                                               ===============       ===============
                                                                             $      1,605,394      $      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                        Six Months Ended
                                                         June 30,                                 June 30,
                                             ---------------------------------        ---------------------------------
                                                 1999               1998                  1999               1998
                                             --------------     --------------        --------------     --------------
<S>                                       <C>                 <C>                  <C>                <C>
REVENUES:
     Oil and gas sales                    $         55,745    $        92,803      $         96,397   $        133,377
     Interest income                                   359              1,799                 2,329              4,136
     Other                                              --                314                    --                543
                                             --------------     --------------        --------------     --------------
                                                    56,104             94,916                98,726            138,056
                                             --------------     --------------        --------------     --------------


COSTS AND EXPENSES:
     Lease operating                                18,821             32,652                33,456             77,198
     Production taxes                                3,396              3,993                 5,435              6,604
     Depreciation, depletion
          and amortization                          26,903             44,904                54,686             68,989
     General and administrative                     22,795             25,741                52,510             63,572
                                             --------------     --------------        --------------     --------------
                                                    71,915            107,290               146,087            216,363
                                             ==============     ==============        ==============     ==============
NET INCOME (LOSS)                         $        (15,811)   $       (12,374)     $        (47,361)  $        (78,307)
                                             ==============     ==============        ==============     ==============




Limited Partners' net income (loss)
     per unit                             $          (1.18)   $         (0.88)     $          (3.35)  $          (5.55)
                                             ==============     ==============        ==============     ==============
</TABLE>


                 See accompanying notes to financial statements.

                                        4


<PAGE>

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


<TABLE>
<CAPTION>
                                                                                             Six Months Ended
                                                                                                 June 30,
                                                                                   -------------------------------------
                                                                                        1999                  1998
                                                                                   ---------------       ---------------
<S>                                                                              <C>                   <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
     Income (loss)                                                               $       (47,361)      $       (78,307)
     Adjustments to reconcile income (loss) to
          net cash provided by operations:
          Depreciation, depletion and amortization                                        54,686                68,989
          Change in gas imbalance receivable
               and deferred revenues                                                          --               (16,719)
          Change in assets and liabilities:
               (Increase) decrease in oil and gas sales receivable                        37,652               241,166
               (Increase) decrease in other current assets                                (2,302)               (2,555)
               Increase (decrease) in accounts payable                                    10,254               (31,231)
                                                                                   ---------------       ---------------
          Net cash provided by (used in) operating activities                             52,929               181,343
                                                                                   ---------------       ---------------

CASH FLOWS FROM INVESTING ACTIVITIES:
     Additions to oil and gas properties                                                  (5,635)              (51,367)
                                                                                   ---------------       ---------------

CASH FLOWS FROM FINANCING ACTIVITIES:
     Cash Distributions to partners                                                      (47,268)             (130,149)
                                                                                   ---------------       ---------------
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                                          26                51,194
                                                                                   ---------------       ---------------
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                                           1,669                 1,173
                                                                                   ===============       ===============
CASH AND CASH EQUIVALENTS AT END OF PERIOD                                       $         1,695      $         52,367
                                                                                   ===============       ===============
</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.  The Managing
        General Partner has either replaced or updated mission  critical systems
        and expects to  complete  testing  during the third  quarter of 1999 and
        continue remedial actions as needed.


                                       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 during the third quarter of 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 $52,929 and $181,343 for the six months
ended June 30, 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
$47,268  and  $130,149  for the  six  months  ended  June  30,  1999  and  1998,
respectively.

      The  Partnership  does  not  allow  for  additional  assessments  from the
partners  to fund  capital  requirements.  However,  funds  are  available  from
partnership  revenues,  borrowings  or  proceeds  from the  sale of  partnership
property.  The  Managing  General  Partners  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 June 30, 1999 (current  quarter) when compared
to the quarter  ended June 30,  1998  (corresponding  quarter),  and for the six
months ended June 30, 1999  (current  period),  when  compared to the six months
ended June 30, 1998 (corresponding period).

Three Months Ended June 30, 1999 and 1998

      Oil and gas sales declined  $37,057 or 40 percent in the second quarter of
1999 when  compared  to the  corresponding  quarter  in 1998,  primarily  due to
decreased  oil and  gas  production.  Current  quarter  oil  and gas  production
declined  53 percent  and 49  percent,  respectively,  when  compared  to second
quarter 1998 production volumes.  The decrease in production  volumes,  from the
partnership's mature wells, had a significant impact on partnership performance.
Oil prices increased 27 percent or $3.32/BBL to an average of $15.81/BBL and gas
prices  increased  17 percent or  $.32/MCF  to an average of  $2.26/MCF  for the
quarter.
                                       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 18 percent in
the second  quarter of 1999  compared to the second  quarter of 1998 while total
production costs decreased 39 percent.

      Associated  depreciation  expense  decreased 40 percent or $18,001 in 1999
compared to second  quarter  1998,  also  related to the  decline in  production
volumes.

Six Months Ended June 30, 1999 and 1998

      Oil and gas sales  declined  $36,981 or 28 percent in the first six months
of 1999 when  compared to the  corresponding  period in 1998,  primarily  due to
decreased oil and gas production. Current period oil and gas production declined
21 percent and 34  percent,  respectively,  when  compared to the same period in
1998. The decrease in production volumes,  from the partnership's  mature wells,
had a significant  impact on partnership  performance.  Oil prices  increased 14
percent or  $1.63/BBL  to an average of  $13.17/BBL  and gas prices  increased 6
percent or $.10/MCF to an average of $1.91/MCF for the current period.

      Corresponding  production costs per equivalent MCF decreased 31 percent in
the first six months of 1999  compared  to the  corresponding  period in 1998 as
total production costs decreased 54 percent.

      Associated  depreciation  expense  decreased 21 percent or $14,303 in 1999
compared  to the first six  months  of 1998,  also  related  to the  decline  in
production volumes.

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

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

                                       11