<PAGE>

                                    FORM 10-Q



                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549


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

                  For the quarterly period ended March 31, 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

                - March 31, 1998 and December 31, 1997                 3

            Statements of Operations

                - Three month periods ended March 31, 1998 and 1997    4

            Statements of Cash Flows

                - Three month periods ended March 31, 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                                          8


SIGNATURES                                                             9
</TABLE>


<PAGE>


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


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

         Current Assets:
              Cash and cash equivalents                                                $      103,057       $        1,173
              Oil and gas sales receivable                                                    213,177              436,486
              Other                                                                             8,799                6,468
                                                                                       ---------------      ---------------
                   Total Current Assets                                                       325,033              444,127
                                                                                       ---------------      ---------------

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

         Oil and Gas Properties, using full cost
              accounting                                                                   12,762,167           12,752,686
         Less-Accumulated depreciation, depletion
              and amortization                                                            (10,701,227)         (10,677,142)
                                                                                       ---------------      ---------------
                                                                                            2,060,940            2,075,544
                                                                                       ---------------      ---------------
                                                                                       $    2,386,319       $    2,519,671
                                                                                       ===============      ===============

         LIABILITIES AND PARTNERS' CAPITAL:

         Current Liabilities:
             Accounts Payable                                                          $      101,279       $       88,549
                                                                                       ---------------      ---------------

         Deferred Revenues                                                                    125,660              125,660

         Limited Partners' Capital (14,121.10 Limited Partnership Units;
                                    $1,000 per unit)                                        2,077,461            2,195,259
         General Partners' Capital                                                             81,919              110,203
                                                                                       ---------------      ---------------
                   Total Partners' Capital                                                  2,159,380            2,305,462
                                                                                       ---------------      ---------------
                                                                                       $    2,386,319       $    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
                                                                                              March 31,
                                                                                 ---------------------------------
                                                                                      1998                   1997
                                                                                 ---------------   ---------------
         <S>                                                                     <C>               <C>
         REVENUES:
             Oil and gas sales                                                   $        40,575   $       154,519
             Interest income                                                               2,337               429
             Other                                                                           229             1,394
                                                                                 ---------------   ---------------
                                                                                          43,141           156,342
                                                                                 ---------------   ---------------
         COSTS AND EXPENSES:
             Lease operating                                                              44,546            48,622
             Production taxes                                                              2,611             7,935
             Depreciation, depletion
               and amortization                                                           24,085            34,884
             General and administrative                                                   37,832            32,596
                                                                                 ---------------   ---------------
                                                                                         109,074           124,037
                                                                                 ---------------   ---------------
         NET INCOME (LOSS)                                                       $       (65,933)  $        32,305
                                                                                 ===============   ===============
</TABLE>


         Limited Partners' net income (loss)
             per unit

         March 31, 1998                       $         (4.67)
                                              ===============
         March 31, 1997                       $          2.29
                                              ===============


                 See accompanying note to financial statements.

                                        4


<PAGE>

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

<TABLE>
<CAPTION>
                                                                                           Three Months Ended
                                                                                                March 31,
                                                                               ----------------------------------------
                                                                                     1998                    1997
                                                                               ---------------          ---------------
<S>                                                                             <C>                     <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
    Income (loss)                                                               $      (65,933)         $        32,305
    Adjustments to reconcile income (loss) to
      net cash provided by operations:
      Depreciation, depletion and amortization                                          24,085                   34,884
      Change in gas imbalance receivable
          and deferred revenues                                                           (346)                    (325)
      Change in assets and liabilities:
        (Increase) decrease in oil and gas sales receivable                            223,309                  (32,696)
        (Increase) decrease in other current assets                                     (2,331)                 105,380
        Increase (decrease) in accounts payable                                         12,730                  (25,563)
                                                                               ---------------          ---------------
                Net cash provided by (used in) operating activities                    191,514                  113,985
                                                                               ---------------          ---------------
CASH FLOWS FROM INVESTING ACTIVITIES:
    Additions to oil and gas properties                                                 (9,481)                  (5,346)
                                                                               ---------------          ---------------
CASH FLOWS FROM FINANCING ACTIVITIES:
    Cash distributions to partners                                                     (80,149)                 (80,557)
                                                                               ---------------          ---------------
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS                                   101,884                   28,082
                                                                               ---------------          ---------------
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD                                         1,173                    1,029
                                                                               ---------------          ---------------
CASH AND CASH EQUIVALENTS AT END OF PERIOD                                      $      103,057          $        29,111
                                                                               ===============          ===============
</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  $191,514 and
$113,985 for the three months ended March 31, 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
the  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   partner's  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 $80,149 and $80,577 for the three months
ended March 31, 1998 and 1997, respectively.

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

Results of Operations

         Oil and gas sales declined  $113,944 or 74 percent in the first 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 51 percent or $1.64/MCF
and in oil  prices  of 51  percent  or  $9.94/BBL  had a  significant  impact on
partnership  performance.  Also, current quarter gas and oil production declined
38 percent and 75 percent,  respectively,  when  compared to first  quarter 1997
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.

         Associated depreciation expense decreased 31 percent or $10,799 in 1998
compared  to first  quarter  1997,  also  related to the  decline in  production
volumes.


                                       7


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


         The  Partnership  records  an  additional  provision  in  depreciation,
depletion and amortization when the present value, discounted at ten percent, of
estimated future net revenues from oil and gas properties,  using the guidelines
of the  Securities  and  Exchange  Commission,  was below the fair market  value
originally paid for oil and gas properties.  Using prices in effect at March 31,
1997, the Partnership  would have recorded an additional  provision at March 31,
1997 in the amount of  $162,964.  However,  these  temporarily  low  quarter-end
prices  rebounded  and by  using  prices  in  effect  at the  filing  date,  the
Partnership's  unamortized  cost of oil and gas  properties  were not limited by
this calculation

         During 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:     May 5, 1998                By:        /s/ John R. Alden
          -----------                           --------------------------------
                                                John R. Alden
                                                Senior Vice President, Secretary
                                                and Principal Financial Officer

Date:     May 5, 1998                By:        /s/ Alton D. Heckaman, Jr.
          -----------                           --------------------------------
                                                Alton D. Heckaman, Jr.
                                                Vice President, Controller
                                                and Principal Accounting Officer


                                        10