<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, 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

                - June 30, 1998 and December 31, 1997                                  3

            Statements of Operations

                - Three month and six month periods ended June 30, 1998 and 1997       4

            Statements of Cash Flows

                - Six month periods ended June 30, 1998 and 1997                       5

            Notes to Financial Statements                                              6

      ITEM 2.    Management's Discussion and Analysis of Financial
                     Condition and Results of Operations                               7

PART II.    OTHER INFORMATION                                                          9


SIGNATURES                                                                            10
</TABLE>


<PAGE>

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



<TABLE>
<CAPTION>
                                                                                           June 30,           December 31,
                                                                                             1998                 1997
                                                                                       ---------------      ---------------
                                                                                         (Unaudited)
         <S>                                                                           <C>                  <C>           
         ASSETS:

         Current Assets:
              Cash and cash equivalents                                                $        1,000       $        1,173
              Oil and gas sales receivable                                                    195,320              436,486
              Other                                                                             9,023                6,468
                                                                                       ---------------      ---------------
                  Total Current Assets                                                        205,343              444,127
                                                                                       ---------------      ---------------

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

         Oil and Gas Properties, using full cost
              accounting                                                                   12,804,053           12,752,686
         Less-Accumulated depreciation, depletion
              and amortization                                                            (10,746,131)         (10,677,142)
                                                                                       ---------------      ---------------
                                                                                            2,057,922            2,075,544
                                                                                       ---------------      ---------------
                                                                                       $    2,263,611       $    2,519,671
                                                                                       ===============      ===============

         LIABILITIES AND PARTNERS' CAPITAL:

         Current Liabilities:
             Accounts Payable                                                          $       57,318       $       88,549
                                                                                       ---------------      ---------------

         Deferred Revenues                                                                    109,287              125,660

         Limited Partners' Capital (14,121.10 Limited Partnership Units;
                                   $1,000 per unit)                                         2,013,045            2,195,259
         General Partners' Capital                                                             83,961              110,203
                                                                                       ---------------      ---------------
                  Total Partners' Capital                                                   2,097,006            2,305,462
                                                                                       ---------------      ---------------
                                                                                       $    2,263,611       $    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                  Six Months Ended
                                                          June 30,                           June 30,
                                              ---------------------------------  ---------------------------------
                                                   1998              1997             1998              1997
                                              ---------------   ---------------  ---------------   ---------------
<S>                                           <C>               <C>              <C>               <C>            
REVENUES:
   Oil and gas sales                          $        92,803   $       105,760  $       133,377   $       260,279
   Interest income                                      1,799               673            4,136             1,102
   Other                                                  314             1,200              543             2,595
                                              ---------------   ---------------  ---------------   ---------------
                                                       94,916           107,633          138,056           263,976
                                              ---------------   ---------------  ---------------   ---------------

COSTS AND EXPENSES:
   Lease operating                                     32,652            53,257           77,198           101,879
   Production taxes                                     3,993             3,651            6,604            11,586
   Depreciation, depletion
      and amortization                                 44,904            39,321           68,989            74,205
   General and administrative                          25,741            30,251           63,572            62,848
                                              ---------------   ---------------  ---------------   ---------------
                                                      107,290           126,480          216,363           250,518
                                              ---------------   ---------------  ---------------   ---------------
NET INCOME (LOSS)                             $       (12,374)  $       (18,847) $       (78,307)  $        13,458
                                              ===============   ===============  ===============   ===============


Limited Partners' net income (loss)
   per unit                                   $          (.88)  $         (1.33) $         (5.55)  $           .95
                                              ===============   ===============  ===============   ===============
</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,
                                                                               ----------------------------------------
                                                                                     1998                    1997
                                                                               ---------------         ----------------
<S>                                                                             <C>                     <C>            
CASH FLOWS FROM OPERATING ACTIVITIES:
    Income (loss)                                                               $      (78,307)         $        13,458
    Adjustments to reconcile income (loss) to
      net cash provided by operations:
      Depreciation, depletion and amortization                                          68,989                   74,205
      Change in gas imbalance receivable
          and deferred revenues                                                        (16,719)                  (1,355)
      Change in assets and liabilities:
        (Increase) decrease in oil and gas sales receivable                            241,166                    1,049
        (Increase) decreae in other current assets                                      (2,555)                      --
        Increase (decrease) in accounts payable                                        (31,231)                 (23,331)
                                                                               ---------------          ---------------
      Net cash provided by (used in) operating activities                              181,343                   64,026
                                                                               ---------------          ---------------
CASH FLOWS FROM INVESTING ACTIVITIES:
    Additions to oil and gas properties                                                (51,367)                  (3,059)
    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                              (51,367)                 104,422
                                                                               ---------------          ---------------
CASH FLOWS FROM FINANCING ACTIVITIES:
    Cash distributions to partners                                                    (130,149)                (168,436)
                                                                               ---------------          ---------------
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                                      (173)                      12
                                                                               ---------------          ---------------
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                                         1,173                    1,029
                                                                               ---------------          ---------------
CASH AND CASH EQUIVALENTS AT END OF PERIOD                                      $        1,000          $         1,041
                                                                               ===============          ===============
</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 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.


                                       6


<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 $181,343 and $64,026 for the six months
ended June 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
$130,149  and  $168,436  for the six  months  ended  June  30,  1998  and  1997,
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, 1998 (current  quarter) when compared
to the quarter  ended June 30,  1997  (corresponding  quarter),  and for the six
months ended June 30, 1998  (current  period),  when  compared to the six months
ended June 30, 1997 (corresponding period).

Three Months Ended June 30, 1998 and 1997

      Oil and gas sales declined  $12,957 or 12 percent in the second quarter of
1998 when  compared  to the  corresponding  quarter  in 1997,  primarily  due to
decreased oil and gas  production.  Oil production  decreased 43 percent and gas
production  declined  6  percent.  The  decrease  in  production  volumes  had a
significant impact on partnership performance. The partnership's sale of several
properties  in the  fourth  quarter  of 1997 had an impact  on 1998  partnership
production  volumes.  Also,  current  quarter oil prices  declined 26 percent or
$4.32/BBL further  contributing to decreased  revenues.  Declines were partially
offset by an increase in gas prices of 11 percent or $.19/MCF  when  compared to
second quarter 1997 prices.

      Associated  depreciation  expense  increased  14 percent or $5,583 in 1998
compared to second quarter 1997.

                                       7

<PAGE>


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


Six Months Ended June 30, 1998 and 1997

      Oil and gas sales declined  $126,902 or 49 percent in the first six 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 $.60/MCF
and in oil  prices  of 37  percent  or  $6.73/BBL  had a  significant  impact on
partnership performance. Also, current period gas and oil production declined 21
percent and 60 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.

      Associated  depreciation  expense  decreased  7 percent  or $5,216 in 1998
compared  to the first six  months  of 1997,  also  related  to the  decline  in
production volumes.

      During 1998,  partnership  revenues  and costs will be shared  between the
limited partners and general partners in a 90:10 ratio.


                                       8


<PAGE>


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




ITEM 5.    OTHER INFORMATION


                                     -NONE-



                                       9


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

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

                                       10