UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549

                                    FORM 10-K

  / x /            Annual Report Pursuant to Section 13 or 15(d)
              of the Securities Exchange Act of 1934 (Fee Required)

                   For the fiscal year ended December 31, 1997

                                       or
  /   /         Transition Report Pursuant to Section 13 or 15(d)
            of the Securities Exchange Act of 1934 (No Fee Required)

                         Commission File No. 33-38582-02

                           PARKER & PARSLEY 91-B, L.P.
             (Exact name of Registrant as specified in its charter)

                Delaware                                     75-2397335
     (State or other jurisdiction of                      (I.R.S. Employer
      incorporation or organization)                   Identification Number)

 303 West Wall, Suite 101, Midland, Texas                       79701
 (Address of principal executive offices)                     (Zip code)

       Registrant's Telephone Number, including area code : (915) 683-4768
        Securities registered pursuant to Section 12(b) of the Act: None
           Securities registered pursuant to Section 12(g) of the Act:
                 Limited partnership interests ($1,000 per unit)

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 / /

Indicate by check mark if disclosure of delinquent  filers  pursuant to Item 405
of Regulation  S-K is not contained  herein,  and will not be contained,  to the
best of Registrant's  knowledge,  in definitive proxy or information  statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. / x /

No  market  currently  exists  for  the  limited  partnership  interests  of the
Registrant.  Based on original  purchase  price the  aggregate  market  value of
limited  partnership  interests  owned by  non-affiliates  of the  Registrant is
$11,239,000.

             As of March 9, 1998, the number of outstanding limited
          partnership interests was 11,249. The following documents are
               incorporated by reference into the indicated parts
                    of this Annual Report on Form 10-K: None



<PAGE>



Parts I and II of this Report contain  forward  looking  statements that involve
risks and uncertainties. Accordingly, no assurances can be given that the actual
events and results will not be materially different than the anticipated results
described  in the  forward  looking  statements.  See "Item 1.  Business"  for a
description of various factors that could  materially  affect the ability of the
Partnership to achieve the anticipated  results described in the forward looking
statements.
                                     PART I

ITEM 1.     Business

Parker &  Parsley  91-B,  L.P.  (the  "Partnership")  is a  limited  partnership
organized in 1991 under the laws of the State of Delaware. As of August 8, 1997,
Pioneer Natural Resources USA, Inc.  ("Pioneer USA") became the managing general
partner of the Partnership.  Prior to August 8, 1997, the Partnership's managing
general  partner  was  Parker  &  Parsley  Petroleum  USA,  Inc.  ("PPUSA"),   a
wholly-owned  subsidiary  of  Parker &  Parsley  Petroleum  Company  ("Parker  &
Parsley").  On August 7, 1997,  Parker & Parsley and Mesa Inc. ("Mesa") received
shareholder  approval  to merge and create  Pioneer  Natural  Resources  Company
("Pioneer").  On August 8, 1997,  PPUSA was merged with and into  Pioneer USA, a
wholly-owned  subsidiary  of  Pioneer,  resulting  in Pioneer USA  becoming  the
managing general partner of the Partnership as PPUSA's successor by merger.  For
a more  complete  description  of the  Parker &  Parsley  and Mesa  merger,  see
Pioneer's  Registration  Statement  on Form S-4 as filed with the  Securities  &
Exchange Commission.

A Registration  Statement,  as amended,  filed pursuant to the Securities Act of
1933,  registering limited partnership  interests  aggregating  $105,000,000 and
$45,000,000  in general  partnership  interests in a series of Delaware  limited
partnerships  formed  under the  Parker &  Parsley  91-92  Development  Drilling
Program,  was declared  effective by the Securities  and Exchange  Commission on
June 25,  1991.  On  December  31,  1991,  the  offering  of limited and general
partnership  interests in the Partnership,  the second  partnership formed under
such statement, was closed, with interests aggregating $11,249,000 being sold to
682  subscribers  of which  $6,675,000  were sold to 380  subscribers as general
partner interests and $4,574,000 were sold to 302 subscribers as limited partner
interests.  The general  partners were converted to limited partners on November
30, 1992.

The Partnership  engages primarily in oil and gas development and production and
is not  involved in any  industry  segment  other than oil and gas. See "Item 6.
Selected  Financial  Data" and "Item 8. Financial  Statements and  Supplementary
Data" of this  report for a summary  of the  Partnership's  revenue,  income and
identifiable assets.

The principal  markets during 1997 for the oil produced by the Partnership  were
refineries  and  oil  transmission  companies  that  have  facilities  near  the
Partnership's   oil  producing   properties.   The  principal  markets  for  the
Partnership's   gas  were  companies  that  have  pipelines   located  near  the
Partnership's gas producing  properties.  Of the Partnership's total oil and gas
revenues for 1997,  approximately  51%, 26% and 19% were  attributable  to sales
made to  Mobil  Oil  Corporation,  Genesis  Crude  Oil,  L.P.  and  Western  Gas
Resources, Inc., respectively.
                                        2

<PAGE>



The Partnership's revenues,  profitability,  cash flow and future rate of growth
are highly dependent on the prevailing prices of oil and gas, which are affected
by numerous  factors  beyond  the  Partnership's  control.  Oil  and  gas prices
historically  have been very volatile.  A substantial or extended decline in the
prices of oil or gas could have a material  adverse effect on the  Partnership's
revenues,  profitability and cash flow and could,  under certain  circumstances,
result in a reduction in the  carrying  value of the  Partnership's  oil and gas
properties.

Because of the demand for oil and gas, the Partnership does not believe that the
termination  of the  sales of its  products  to any one  customer  would  have a
material adverse impact on its operations. The loss of a particular customer for
gas may have an effect if that  particular  customer  has the only gas  pipeline
located  in the  areas  of  the  Partnership's  gas  producing  properties.  The
Partnership  believes,  however,  that  the  effect  would be  temporary,  until
alternative arrangements could be made.

Federal and state  regulation of oil and gas operations  generally  includes the
fixing of maximum prices for regulated categories of natural gas, the imposition
of maximum  allowable  production rates, the taxation of income and other items,
and the protection of the  environment.  Although the Partnership  believes that
its business operations do not impair  environmental  quality and that its costs
of complying with any  applicable  environmental  regulations  are not currently
significant,   the  Partnership  cannot  predict  what,  if  any,  effect  these
environmental regulations may have on its current or future operations.

The  Partnership  does not have any  employees  of its own.  Pioneer USA employs
1,133 persons, many of whom dedicated a part of their time to the conduct of the
Partnership's business during the period for which this report is filed. Pioneer
USA is responsible for all management functions.

Numerous  uncertainties  exist in estimating  quantities of proved  reserves and
future net revenues  therefrom.  The  estimates  of proved  reserves and related
future net revenues  set forth in this report are based on various  assumptions,
which may ultimately  prove to be inaccurate.  Therefore,  such estimates should
not be construed as estimates of the current  market value of the  Partnership's
proved reserves.

No material part of the  Partnership's  business is seasonal and the Partnership
conducts no foreign operations.

ITEM 2.     Properties

The  Partnership's  properties  consist  primarily  of  leasehold  interests  in
properties on which oil and gas wells are located.  Such property  interests are
often subject to landowner royalties, overriding royalties and other oil and gas
leasehold interests.

Fractional  working  interests in  developmental  oil and gas prospects  located
primarily  in the  Spraberry  Trend  Area of West  Texas  were  acquired  by the
Partnership,  resulting in the Partnership's participation in the drilling of 29
oil and gas wells.  At December 31, 1997, the  Partnership  had 29 producing oil
and gas wells.
                                        3

<PAGE>



For  information  relating  to the  Partnership's  estimated  proved oil and gas
reserves at December 31, 1997,  1996 and 1995,  see Note 7 of Notes to Financial
Statements  included in "Item 8. Financial  Statements and  Supplementary  Data"
below. Such reserves have been estimated by the engineering staff of Pioneer USA
with a review by an independent petroleum consultant.

ITEM 3.     Legal Proceedings

The  Partnership  is a party to  various  legal  proceedings  incidental  to its
business  involving claims in oil and gas leases or interests,  other claims for
damages in amounts not in excess of 10% of its current assets and other matters,
none of which Pioneer believes to be material.

ITEM 4.     Submission of Matters to a Vote of Security Holders

There were no matters  submitted to a vote of security holders during the fourth
quarter of 1997.



                                        4

<PAGE>



                                     PART II


ITEM 5.     Market for Partnership's Common Equity and Related Stockholder
             Matters

At March 9, 1998, the Partnership  had 11,249  outstanding  limited  partnership
interests  held of record by 677  subscribers.  There is no  established  public
trading  market  for  the  limited  partnership  interests.  Under  the  limited
partnership  agreement,  Pioneer USA has made  certain  commitments  to purchase
partnership interests at a computed value.

Revenues which, in the sole judgement of the managing general  partner,  are not
required  to meet  the  Partnership's  obligations  will be  distributed  to the
partners  at  least  quarterly  in  accordance  with  the  limited   partnership
agreement.  During the years  ended  December  31, 1997 and 1996,  $847,290  and
$949,416,  respectively,  of such revenue-related distributions were made to the
limited partners.

ITEM 6.     Selected Financial Data

The  following  table sets forth  selected  financial  data for the years  ended
December 31:
<TABLE>
                                   1997         1996         1995         1994         1993
                                ----------   ----------   ----------   ----------   -----------
<S>                             <C>          <C>          <C>          <C>          <C>
Operating results:
  Oil and gas sales             $1,273,373   $1,632,595   $1,416,748   $1,325,311   $ 1,741,007
                                 =========    =========    =========    =========    ==========
  Impairment of oil and gas
    properties                  $  323,078   $      -     $  104,290   $      -     $ 4,438,849
                                 =========    =========    =========    =========    ==========
  Net income (loss)             $  222,730   $  924,002   $  483,679   $  466,370   $(4,507,647)
                                 =========    =========    =========    =========    ==========
  Allocation of net income
    (loss):
     Managing general partner   $    2,227   $    9,240   $    4,837   $    4,664   $   (45,076)
                                 =========    =========    =========    =========    ==========
     Limited partners           $  220,503   $  914,762   $  478,842   $  461,706   $(4,462,571)
                                 =========    =========    =========    =========    ==========
  Net income (loss) per
    limited partners' interest  $    19.60   $    81.32   $    42.57   $    41.04   $   (396.71)
                                 =========    =========    =========    =========    ==========
  Limited partners' cash
    distributions per limited
    partners' interest          $    75.32   $    84.40   $    70.24   $    46.96   $    103.99
                                 =========    =========    =========    =========    ==========
At year end:
  Total assets                  $2,424,808   $3,051,464   $3,131,023   $3,404,388   $ 3,603,345
                                 =========    =========    =========    =========    ==========
</TABLE>
                                        5

<PAGE>




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

Results of Operations

1997 compared to 1996

The  Partnership's  1997 oil and gas revenues  decreased 22% to $1,273,373  from
$1,632,595  in  1996.  The  decrease  in  revenues  resulted  from  declines  in
production and lower average prices  received.  In 1997,  49,485 barrels of oil,
7,536  barrels of natural gas liquids  ("NGLs") and 90,255 mcf of gas were sold,
or 72,064 barrel of oil equivalents ("BOEs"). In 1996, 59,195 barrels of oil and
122,758 mcf of gas were sold, or 79,655 BOEs.

Consistent with the managing general  partner,  the Partnership has historically
accounted for processed  natural gas production as wellhead  production on a wet
gas basis. As a result of the merger with Mesa, the managing general partner has
adopted  Mesa's  accounting  policy and now accounts for  processed  natural gas
production  in two  components:  natural gas  liquids and dry residue  gas. As a
result of the change in the managing general partner's  policy,  the Partnership
now accounts  for  processed  natural gas  production  as processed  natural gas
liquids and dry residue gas. Consequently,  separate product volumes will not be
comparable for periods prior to September 30, 1997.

The declines in production  volumes were primarily  attributable  to the decline
characteristics  of the Partnership's  oil and gas properties.  Because of these
characteristics, management expects a certain amount of decline in production to
continue in the future until the Partnership's economically recoverable reserves
are fully depleted.

The average price received per barrel of oil decreased $1.96, or 9%, from $21.73
in 1996 to $19.77 in 1997.  The average  price  received  per barrel of NGLs was
$10.54 in 1997.  The average  price  received per mcf of gas  decreased 15% from
$2.82  in 1996 to  $2.39  in 1997.  The  market  price  for oil and gas has been
extremely  volatile in the past decade,  and management expects a certain amount
of  volatility  to continue  in the  foreseeable  future.  The  Partnership  may
therefore  sell its future oil and gas  production  at average  prices  lower or
higher than that received in 1997.

Gain on disposition of assets of $7,879,  recognized during 1997,  resulted from
proceeds  received  on the sale of mineral  rights on an  undeveloped  property.
During  1996,  a loss on  disposition  of  assets of  $1,221  resulted  from the
abandonment of a saltwater disposal well.

Total costs and expenses increased in 1997 to $1,072,064 as compared to $720,918
in 1996, an increase of $351,146, or 49%. The increase was due to the impairment
of oil and gas properties and increases in production costs, offset by decreases
in depletion, general and administrative expenses ("G&A") and abandoned property
costs.
                                        6

<PAGE>



Production  costs were  $524,112 in 1997 and  $471,736 in 1996,  resulting  in a
$52,376  increase,  or 11%.  This  increase  was due to higher well  maintenance
costs, ad valorem taxes and workover expenses, offset by a decline in production
taxes.

G&A's  components are independent  accounting and engineering  fees and managing
general  partner  personnel  and  operating  costs.   During  this  period,  G&A
decreased,  in  aggregate,  17% from  $47,177 in 1996 to  $39,082  in 1997.  The
Partnership  paid the managing  general  partner  $35,160 in 1997 and $31,806 in
1996 for G&A incurred on behalf of the Partnership.  G&A is allocated,  in part,
to the Partnership by the managing general partner.  Such allocated expenses are
determined by the managing general partner based upon its judgement of the level
of  activity  of the  Partnership  relative to the  managing  general  partner's
activities in other entities it manages.  The method of allocation has varied in
certain  years and may do so again  depending on the  activities of the managing
entities.

The Partnership  adopted  Statement of Financial  Accounting  Standards No. 121,
"Accounting for the Impairment of Long-Lived Assets and for Long-Lived Assets to
be Disposed Of" ("SFAS 121")  effective as of October 1, 1995 (see Notes 2 and 3
of Notes to Financial  Statements included in "Item 8. Financial  Statements and
Supplementary Data"). As a result of the review and evaluation of its long-lived
assets for impairment,  the Partnership recognized a non-cash charge of $323,078
related to its oil and gas properties during the fourth quarter of 1997.

Depletion was $185,792 in 1997 compared to $201,563 in 1996. This  represented a
decrease of $15,771,  or 8%. This  decrease was  primarily  attributable  to the
reduction  in oil  production  of 9,710  barrels  for 1997 as  compared to 1996,
offset by a decrease in oil reserves  during 1997 as a result of lower commodity
prices.

Abandoned  property  costs  associated  with the  abandonment  of one  saltwater
disposal well during 1996 totaled $442.

1996 compared to 1995

The  Partnership's  1996  oil and gas  revenues  increased  to  $1,632,595  from
$1,416,748 in 1995,  an increase of 15%. The increase in revenues  resulted from
higher  average  prices  received  per  barrel of oil and mcf of gas,  offset by
declines in barrels of oil and mcf of gas  produced  and sold.  In 1996,  59,195
barrels  of oil were  sold  compared  to  65,782 in 1995,  a  decrease  of 6,587
barrels,  or 10%. In 1996,  122,758 mcf of gas were sold  compared to 132,724 in
1995,  a decrease of 9,966 mcf, or 8%. The declines in  production  volumes were
primarily  attributable to the decline  characteristics of the Partnership's oil
and gas properties.

The average  price  received per barrel of oil  increased  $4.20,  or 24%,  from
$17.53 in 1995 to $21.73 in 1996.  The  average  price  received  per mcf of gas
increased 42% from $1.99 in 1995 to $2.82 in 1996.

Loss on  disposition  of assets of $1,221  resulted  from the  abandonment  of a
saltwater disposal well during 1996.

                                        7

<PAGE>



Total costs and  expenses  decreased in 1996 to $720,918 as compared to $945,093
in 1995,  a decrease of  $224,175,  or 24%.  The decrease was due to declines in
production costs, depletion and impairment of oil and gas properties,  offset by
increases in G&A and abandoned property costs.

Production  costs were  $471,736 in 1996 and  $531,423 in 1995,  resulting  in a
$59,687  decrease,  or 11%.  This decrease was due to a reduction in well repair
and maintenance  costs and workover  costs,  offset by higher  production  taxes
resulting from increased oil and gas sales.

During this period,  G&A  increased,  in aggregate,  29% from $36,638 in 1995 to
$47,177 in 1996. The  Partnership  paid the managing  general partner $31,806 in
1996 and $31,570 in 1995 for G&A incurred on behalf of the Partnership.

The  Partnership  adopted SFAS 121  effective as of October 1, 1995 (see Notes 2
and 3 of Notes to Financial Statements included in "Item 8. Financial Statements
and  Supplementary  Data").  As a result of the  review  and  evaluation  of its
long-lived assets for impairment,  the Partnership  recognized a non-cash charge
of $104,290  related to its oil and gas properties  during the fourth quarter of
1995.

Depletion was $201,563 in 1996 compared to $272,742 in 1995. This  represented a
decrease of $71,179,  or 26%. This decrease was  primarily  attributable  to the
following  factors:  (i) a reduction in the  Partnership's  net depletable basis
from  charges  taken in  accordance  with  SFAS  121,  (ii) a  reduction  in oil
production of 6,587 barrels for 1996 as compared to 1995,  and (iii) an increase
in oil and gas reserves during 1996 as a result of higher commodity prices.

Abandoned  property  costs  associated  with the  abandonment  of one  saltwater
disposal well during 1996 totaled $442.

Impact of inflation and changing prices on sales and net income

Inflation  impacts  the fixed  overhead  rate  charges  of the  lease  operating
expenses for the  Partnership.  During 1995,  the annual  change in the index of
average weekly earnings of crude petroleum and gas production  workers issued by
the U.S. Department of Labor, Bureau of Labor Statistics  increased by 4.4%. The
1996 annual change in average weekly earnings  increased by 4.1%. The 1997 index
(effective  April 1, 1997) increased 2%. The impact of inflation for other lease
operating  expenses is small due to the current  economic  condition  of the oil
industry.

The oil and gas industry  experienced  volatility during the past decade because
of the fluctuation of the supply of most fossil fuels relative to the demand for
such  products  and other  uncertainties  in the world  energy  markets  causing
significant  fluctuations  in oil and gas  prices.  During  1997,  the price per
barrel for oil production similar to the Partnership's ranged from approximately
$16.00 to $23.00. During most of 1997 and 1996, the Partnership  benefitted from
higher oil prices as  compared  to previous  years.  However,  during the fourth
quarter of 1997, oil prices began a downward trend that has continued into March
1998. On March 19, 1998, the market price for West Texas  intermediate crude was

                                        8

<PAGE>


$12.00 per  barrel.  A  continuation  of the oil price  environment  experienced
during  the  first  quarter  of  1998  will  have  an  adverse   effect  on  the
Partnership's  revenues and  operating  cash flow and could result in additional
decreases in the carrying value of the Partnership's oil and gas properties.

Prices for natural gas are subject to ordinary seasonal  fluctuations,  and this
volatility of natural gas prices may result in production  being  curtailed and,
in some cases, wells being completely shut-in.

Liquidity and capital resources

Net Cash Provided by Operating Activities

Net cash provided by operating  activities  decreased  $188,887  during the year
ended  December 31, 1997 from the year ended December 31, 1996. The decrease was
primarily attributable to a decline in oil and gas sales receipts.

Net Cash Provided by (Used in) Investing Activities

The  Partnership's  principal  investing  activities  during  1997 and 1996 were
related  to the  addition  or  disposal  of  equipment  on  various  oil and gas
properties.

Proceeds from asset  dispositions  of $7,879  received during 1997 resulted from
the sale of mineral rights on an undeveloped property.

Net Cash Used in Financing Activities

Cash  available  was  sufficient  in 1997 for  distributions  to the partners of
$855,848 of which $8,558 was  distributed  to the managing  general  partner and
$847,290 to the limited partners. In 1996, cash was sufficient for distributions
to the  partners of $959,006 of which  $9,590 was  distributed  to the  managing
general partner and $949,416 to the limited partners.

It is expected that future net cash  provided by  operations  will be sufficient
for any capital  expenditures and any distributions.  As the production from the
properties declines, distributions are also expected to decrease.

Information systems for the year 2000

The general partner will be required to modify its information  systems in order
to accurately process Partnership data referencing the year 2000. Because of the
importance of occurrence dates in the oil and gas industry,  the consequences of
not pursuing these  modifications could be very significant to the Partnership's
ability  to manage and  report  operating  activities.  Currently,  the  general
partner plans to contract with third parties to perform the software programming
changes necessary to correct any existing deficiencies. Such programming changes
are  anticipated  to be  completed  and  tested by March 1, 1999.  The  managing
general  partner  will  allocate  a  portion  of  the  costs  of the  year  2000
programming  charges  to the  Partnership  when they are  incurred,  along  with
recurring  general  and  administrative  expenses  as  defined  pursuant  to the
partnership  agreement.  Although the costs are not estimable at this time, they
should not be significant to the Partnership.

                                        9

<PAGE>



ITEM 8.     Financial Statements and Supplementary Data



                          Index to Financial Statements

                                                                          Page

Financial Statements of Parker & Parsley 91-B, L.P.:
  Independent Auditors' Report..........................................   11
  Balance Sheets as of December 31, 1997 and 1996.......................   12
  Statements of Operations for the Years Ended December 31,
    1997, 1996 and 1995.................................................   13
  Statements of Partners' Capital for the Years Ended
    December 31, 1997, 1996 and 1995....................................   14
  Statements of Cash Flows for the Years Ended December 31,
    1997, 1996 and 1995.................................................   15
  Notes to Financial Statements.........................................   16



                                       10

<PAGE>




                          INDEPENDENT AUDITORS' REPORT




The Partners
Parker & Parsley 91-B, L.P.
  (A Delaware Limited Partnership):

We have  audited the  financial  statements  of Parker & Parsley  91-B,  L.P. as
listed  in  the  accompanying   index.   These  financial   statements  are  the
responsibility of the Partnership's management. Our responsibility is to express
an opinion on these financial statements based on our audits.

We  conducted  our  audits  in  accordance  with  generally   accepted  auditing
standards.  Those standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement.  An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements.  An audit also includes
assessing the  accounting  principles  used and  significant  estimates  made by
management,  as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.

In our opinion,  the financial  statements  referred to above present fairly, in
all material respects,  the financial position of Parker & Parsley 91-B, L.P. as
of December 31, 1997 and 1996,  and the results of its  operations  and its cash
flows for each of the years in the three-year period ended December 31, 1997, in
conformity with generally accepted accounting principles.

As  discussed  in Notes 2 and 3 to the  financial  statements,  the  Partnership
adopted the provisions of the Financial  Accounting  Standards Board's Statement
of Financial  Accounting  Standards No. 121,  "Accounting  for the Impairment of
Long-Lived Assets and for Long-Lived Assets to Be Disposed Of" in 1995.




                                                 KPMG Peat Marwick LLP

Midland, Texas
March 20, 1998



                                       11

<PAGE>



                           PARKER & PARSLEY 91-B, L.P.
                        (A Delaware Limited Partnership)

                                 BALANCE SHEETS
                                   December 31


                                                    1997            1996
                                                 -----------     ----------
                  ASSETS

Current assets:
  Cash and cash equivalents, including
     interest bearing deposits of $199,947
     in 1997 and $236,894 in 1996                $   200,122     $   237,013
  Accounts receivable - oil and gas sales            136,917         225,511
                                                  ----------      ----------
          Total current assets                       337,039         462,524
                                                  ----------      ----------
Oil and gas properties - at cost, based on the
  successful efforts accounting method             9,704,606       9,696,907
Accumulated depletion                             (7,616,837)     (7,107,967)
                                                  ----------      ----------
          Net oil and gas properties               2,087,769       2,588,940
                                                  ----------      ----------
                                                 $ 2,424,808     $ 3,051,464
                                                  ==========      ==========
LIABILITIES AND PARTNERS' CAPITAL

Current liabilities:
  Accounts payable - affiliate                   $    27,110     $    20,648

Partners' capital:
  Managing general partners                           20,944          27,275
  Limited partners (11,249 interests)              2,376,754       3,003,541
                                                  ----------      ----------
                                                   2,397,698       3,030,816
                                                  ----------      ----------
                                                 $ 2,424,808     $ 3,051,464
                                                  ==========      ==========


   The accompanying notes are an integral part of these financial statements.

                                       12

<PAGE>



                           PARKER & PARSLEY 91-B, L.P.
                        (A Delaware Limited Partnership)

                            STATEMENTS OF OPERATIONS
                         For the years ended December 31



                                              1997         1996         1995
                                           ----------   ----------   ----------
Revenues:
  Oil and gas                              $1,273,373   $1,632,595   $1,416,748
  Interest and other                           13,542       13,546       12,024
  Gain (loss) on disposition of assets          7,879       (1,221)         -
                                            ---------    ---------    ---------
                                            1,294,794    1,644,920    1,428,772
                                            ---------    ---------    ---------
Costs and expenses:
  Oil and gas production                      524,112      471,736      531,423
  General and administrative                   39,082       47,177       36,638
  Impairment of oil and gas properties        323,078          -        104,290
  Depletion                                   185,792      201,563      272,742
  Abandoned property                              -            442          -
                                            ---------    ---------    ---------
                                            1,072,064      720,918      945,093
                                            ---------    ---------    ---------
Net income                                 $  222,730   $  924,002   $  483,679
                                            =========    =========    =========
Allocation of net income:
  Managing general partner                 $    2,227   $    9,240   $    4,837
                                            =========    =========    =========
  Limited partners                         $  220,503   $  914,762   $  478,842
                                            =========    =========    =========
Net income per limited partners' interest  $    19.60   $    81.32   $    42.57
                                            =========    =========    =========


   The accompanying notes are an integral part of these financial statements.

                                       13

<PAGE>



                           PARKER & PARSLEY 91-B, L.P.
                        (A Delaware Limited Partnership)

                         STATEMENTS OF PARTNERS' CAPITAL



                                             Managing
                                             general     Limited
                                             partner     partners       Total
                                            ---------   ----------   ----------

Partners' capital at January 1, 1995        $  30,859   $3,349,475   $3,380,334

    Distributions                              (8,071)    (790,122)    (798,193)

    Net income                                  4,837      478,842      483,679
                                             --------    ---------    ---------
Partners' capital at December 31, 1995         27,625    3,038,195    3,065,820

    Distributions                              (9,590)    (949,416)    (959,006)

    Net income                                  9,240      914,762      924,002
                                             --------    ---------    ---------
Partners' capital at December 31, 1996         27,275    3,003,541    3,030,816

    Distributions                              (8,558)    (847,290)    (855,848)

    Net income                                  2,227      220,503      222,730
                                             --------    ---------    ---------
Partners' capital at December 31, 1997      $  20,944   $2,376,754   $2,397,698
                                             ========    =========    =========



   The accompanying notes are an integral part of these financial statements.

                                       14

<PAGE>



                           PARKER & PARSLEY 91-B, L.P.
                        (A Delaware Limited Partnership)

                            STATEMENTS OF CASH FLOWS
                         For the years ended December 31


                                               1997        1996        1995
                                            ---------   ----------   ---------
Cash flows from operations:
  Net income                                $ 222,730   $  924,002   $ 483,679
  Adjustments to reconcile net income to
   net cash provided by operations:
     Impairment of oil and gas properties     323,078          -       104,290
     Depletion                                185,792      201,563     272,742
     (Gain) loss on disposition of assets      (7,879)       1,221         -
  Changes in assets and liabilities:
     Accounts receivable                       88,594      (75,782)    (18,635)
     Accounts payable                           6,462      (43,340)     39,928
                                             --------    ---------    --------
          Net cash provided by operating
            activities                        818,777    1,007,664     882,004
                                             --------    ---------    --------
Cash flows from investing activities:
  Additions to oil and gas properties          (7,699)        (721)    (17,890)
  Proceeds from asset dispositions              7,879          -           -
                                             --------    ---------    --------
          Net cash provided by (used in)
            investing activities                  180         (721)    (17,890)
                                             --------    ---------    --------
Cash flows from financing activities:
  Cash distributions to partners             (855,848)    (959,006)   (798,193)
                                             --------    ---------    --------
Net increase (decrease) in cash and cash
  equivalents                                 (36,891)      47,937      65,921
Cash and cash equivalents at beginning
  of year                                     237,013      189,076     123,155
                                             --------    ---------    --------
Cash and cash equivalents at end of year    $ 200,122   $  237,013   $ 189,076
                                             ========    =========    ========

   The accompanying notes are an integral part of these financial statements.

                                       15

<PAGE>


                           PARKER & PARSLEY 91-B, L.P.
                        (A Delaware Limited Partnership)

                          NOTES TO FINANCIAL STATEMENTS
                        December 31, 1997, 1996 and 1995

Note 1.     Organization and nature of operations

       Parker & Parsley 91-B, L.P. (the  "Partnership") is a limited partnership
organized in 1991 under the laws of the State of Delaware. As of August 8, 1997,
Pioneer Natural Resources USA, Inc.  ("Pioneer USA") became the managing general
partner of the Partnership.  Prior to August 8, 1997, the Partnership's managing
general  partner  was  Parker  &  Parsley  Petroleum  USA,  Inc.  ("PPUSA"),   a
wholly-owned  subsidiary  of  Parker &  Parsley  Petroleum  Company  ("Parker  &
Parsley").  On  August  7,  1997,  Parker  &  Parsley  and  Mesa  Inc.  received
shareholder  approval  to merge and create  Pioneer  Natural  Resources  Company
("Pioneer").  On August 8, 1997,  PPUSA was merged with and into  Pioneer USA, a
wholly-owned  subsidiary  of  Pioneer,  resulting  in Pioneer USA  becoming  the
managing general partner of the Partnership as PPUSA's successor by merger.

       The  Partnership  engages  primarily  in  oil  and  gas  development  and
production  in Texas and is not involved in any industry  segment other than oil
and gas.

Note 2.     Summary of significant accounting policies

       A summary of the significant  accounting policies consistently applied in
the preparation of the accompanying financial statements follows:

       The Partnership  accounts for long-lived  assets to be disposed of at the
lower of their carrying  amount or fair value less costs to sell once management
has committed to a plan to dispose of the assets.

       Oil and gas properties - The Partnership  utilizes the successful efforts
method of accounting for its oil and gas  properties  and equipment.  Under this
method, all costs associated with productive wells and nonproductive development
wells are  capitalized  while  nonproductive  exploration  costs  are  expensed.
Capitalized   costs  relating  to  proved  properties  are  depleted  using  the
unit-of-production  method on a  property-by-property  basis based on proved oil
(dominant  mineral)  reserves as determined by the engineering  staff of Pioneer
USA, the  Partnership's  managing general  partner,  and reviewed by independent
petroleum  consultants.  The carrying  amounts of  properties  sold or otherwise
disposed of and the related  allowances  for depletion are  eliminated  from the
accounts and any gain or loss is included in operations.

       Impairment  of  long-lived  assets  - In  accordance  with  Statement  of
Financial  Accounting  Standards  No. 121,  "Accounting  for the  Impairment  of
Long-Lived Assets and for Long-Lived Assets to be Disposed Of" ("SFAS 121"), the
Partnership  reviews its long-lived  assets to be held and used on an individual
property  basis,  including  oil and gas  properties  accounted  for  under  the
successful  efforts  method of  accounting,  whenever  events  or  circumstances
indicate  that the  carrying  value of those assets may not be  recoverable.  An
impairment  loss is  indicated if  the sum of the  expected future cash flows is

                                       16

<PAGE>


less  than  the  carrying  amount  of the  assets.  In  this  circumstance,  the
Partnership  recognizes an impairment  loss for the amount by which the carrying
amount of the asset exceeds the fair value of the asset.

       Use of estimates in the preparation of financial statements - Preparation
of the accompanying  financial  statements in conformity with generally accepted
accounting principles requires management to make estimates and assumptions that
affect  the  reported  amounts  of assets  and  liabilities  and  disclosure  of
contingent  assets and  liabilities at the date of the financial  statements and
the  reporting  amounts of revenues and expenses  during the  reporting  period.
Actual results could differ from those estimates.

       Net income per limited partnership  interest - The net income per limited
partnership  interest is calculated by using the number of  outstanding  limited
partnership interests.

       Income taxes - A Federal  income tax  provision  has not been included in
the  financial  statements as the income of the  Partnership  is included in the
individual Federal income tax returns of the respective partners.

       Statements of cash flows - For purposes of reporting cash flows, cash and
cash equivalents include depository accounts held by banks.

       General and administrative expenses - General and administrative expenses
are allocated in part to the Partnership by the managing  general partner or its
affiliates.  Such  allocated  expenses are  determined  by the managing  general
partner  based upon its  judgement  of the level of activity of the  Partnership
relative to the managing  general  partner's  activities  and other  entities it
manages.  The method of  allocation  has  varied in certain  years and may do so
again depending on the activities of the managed entities.

       Reclassifications - Certain  reclassifications have been made to the 1996
and  1995  financial  statements  to  conform  to the 1997  financial  statement
presentation.

       Environmental  - The Partnership is subject to extensive  federal,  state
and local  environmental laws and regulations.  These laws, which are constantly
changing,  regulate  the  discharge of materials  into the  environment  and may
require the Partnership to remove or mitigate the  environmental  effects of the
disposal  or release of  petroleum  or  chemical  substances  at various  sites.
Environmental expenditures are expensed or capitalized depending on their future
economic benefit.  Expenditures  that relate to an existing  condition caused by
past  operations  and  that  have no  future  economic  benefits  are  expensed.
Liabilities  for   expenditures  of  a  noncapital   nature  are  recorded  when
environmental  assessment and/or  remediation is probable,  and the costs can be
reasonably  estimated.  Such liabilities are generally  undiscounted  unless the
timing of cash  payments for the  liability  or component  are fixed or reliably
determinable.

Note 3.     Impairment of long-lived assets

       The Partnership  adopted SFAS 121 effective  October 1, 1995. In order to
determine  whether an impairment  has occurred,  the  Partnership  estimates the

                                       17

<PAGE>

expected  future  cash flows of its oil and gas  properties  and  compares  such
future  cash flows  to the  carrying  amount  of the oil  and gas  properties to
determine  if the  carrying  amount  is  recoverable.  For  those  oil  and  gas
properties  for which the carrying  amount  exceeded the  estimated  future cash
flows,  an  impairment  was  determined  to exist;  therefore,  the  Partnership
adjusted the carrying amount of those oil and gas properties to their fair value
as determined by discounting their expected future cash flows at a discount rate
commensurate with the risks involved in the industry.  As a result of the review
and  evaluation  of  its  long-lived  assets  for  impairment,  the  Partnership
recognized  non-cash charges of $323,078 and $104,290 related to its oil and gas
properties during the fourth quarters of 1997 and 1995, respectively.

Note 4.     Income taxes

       The  financial  statement  basis  of the  Partnership's  net  assets  and
liabilities was $378,510 greater than the tax basis at December 31, 1997.

       The  following  is a  reconciliation  of net  income  per  statements  of
operations  with the net income per  Federal  income tax  returns  for the years
ended December 31:
                                                1997        1996        1995
                                              ---------   ---------   ---------
 Net income per statements of operations      $ 222,730   $ 924,002   $ 483,679
 Depletion and depreciation provisions for
    tax reporting purposes over amounts
    for financial reporting purposes           (224,519)   (257,785)   (354,761)
 Impairment of oil and gas properties for
    financial reporting purposes                323,078         -       104,290
 Salvage income                                   6,755       1,373       1,601
 Other                                              436         278         -
                                               --------    --------    --------
    Net income per Federal income tax returns $ 328,480   $ 667,868   $ 234,809
                                               ========    ========    ========

Note 5.     Oil and gas producing activities

       The following is a summary of the net costs incurred, whether capitalized
or expensed,  related to the Partnership's oil and gas producing  activities for
the years ended December 31:
                                                1997        1996        1995
                                              --------    --------    --------
       Development costs                      $  7,699    $    (58)   $ 19,111
                                               =======     =======     =======

       Capitalized oil and gas properties consist of the following:
                                                   1997              1996
                                                -----------      -----------
    Property acquisition costs                  $   949,486      $   949,486
    Completed wells and equipment                 8,755,120        8,747,421
                                                 ----------       ----------
                                                  9,704,606        9,696,907
          Accumulated depletion                  (7,616,837)      (7,107,967)
                                                 ----------       ----------
          Net capitalized costs                 $ 2,087,769      $ 2,588,940
                                                 ==========       ==========
                                       18

<PAGE>


       During 1997,  the  Partnership  recognized a non-cash  charge of $323,078
against oil and gas properties associated with SFAS 121. See Note 3.

Note 6.     Related party transactions

       Pursuant to the limited  partnership  agreement,  the Partnership had the
following  related party  transactions  with the managing general partner or its
affiliates during the years ended December 31:
                                                  1997        1996        1995
                                                --------    --------    --------
   Payment of lease operating and
      supervision charges in accordance
      with standard industry operating
      agreements                                $194,622    $176,738    $158,487

   Reimbursement of general and
      administrative expenses                   $ 35,160    $ 31,806    $ 31,570

   Receipt of proceeds for the salvage
      value of retired oil and gas equipment    $    -      $    412    $    -

   Purchase of oil and gas properties and
      related equipment, at predecessor cost    $  1,623    $    -      $ 16,310

       The Partnership  participates in oil and gas activities through an income
tax partnership (the "Program") pursuant to the Program agreement.  Pioneer USA,
P&P Employees 91-B GP ("EMPL") (the  "Entities") and the Partnership are parties
to the  Program  agreement.  EMPL is a  general  partnership  organized  for the
benefit of certain employees of Pioneer USA.

       The costs and  revenues of the Program are  allocated to the Entities and
the Partnership as follows:
                                                    Entities     Partnership (1)
                                                   -----------   ---------------
  Revenues:
    Proceeds from disposition of depreciable
      and depletable properties                    34.3434343%     65.6565657%
    All other revenues                             34.3434343%     65.6565657%
  Costs and expenses:
    Lease acquisition costs, drilling and
      completion costs and all other costs         24.2424242%     75.7575758%
    Operating costs, reporting and legal expenses
      and general and administrative expenses      34.3434343%     65.6565657%

    (1)   Includes Pioneer USA's 1% general partner ownership which is allocated
          at  the Partnership  level and  10 limited  partner interests owned by
          Pioneer USA.

Note 7.     Oil and gas information (unaudited)

       The following  table presents  information relating  to the Partnership's
estimated  proved oil and gas reserves at December  31, 1997,  1996 and 1995 and

                                       19

<PAGE>


changes in such quantities during the years then ended. All of the Partnership's
reserves are  proved and  located within  the United  States.  The Partnership's
reserves are based on an evaluation prepared by the engineering staff of Pioneer
USA  and  reviewed  by  an  independent  petroleum  consultant,  using  criteria
established by the Securities and Exchange Commission. Reserve value information
is available to limited  partners  pursuant to the  Partnership  agreement  and,
therefore, is not presented.
                                                    Oil and NGLs       Gas
                                                       (bbls)         (mcf)
                                                     ----------     ----------
       Net proved reserves at January 1, 1995           693,344      1,648,075
       Revisions                                        181,794        308,877
       Production                                       (65,782)      (132,724)
                                                     ----------     ----------
       Net proved reserves at December 31, 1995         809,356      1,824,228
       Revisions                                        101,417        333,217
       Production                                       (59,195)      (122,758)
                                                     ----------     ----------
       Net proved reserves at December 31, 1996         851,578      2,034,687
       Revisions                                          9,311     (1,177,065)
       Production                                       (57,021)       (90,255)
                                                     ----------     ----------
       Net proved reserves at December 31, 1997         803,868        767,367
                                                     ==========     ==========

       The estimated  present  value of future net revenues of proved  reserves,
calculated  using  December 31, 1997 prices of $17.17 per barrel of oil,  $12.54
per barrel of NGLs and $2.18 per mcf of gas, discounted at 10% was approximately
$3,268,000 and undiscounted  was $5,757,000 at December 31, 1997.  Subsequent to
December 31, 1997, the prices of oil and gas have been  declining,  and on March
19,  1998,  the  average  prices  for  the   Partnership's   oil  and  gas  were
approximately $12.00 and $2.05, respectively.

       The  Partnership   emphasizes  that  reserve   estimates  are  inherently
imprecise  and,  accordingly,  the  estimates  are  expected to change as future
information becomes available.

Note 8.     Major customers

       The following table reflects the major customers of the Partnership's oil
and gas sales (a major  customer is defined as a customer whose sales exceed 10%
of total sales) during the periods ended December 31:
                                                    1997       1996       1995
                                                  --------   --------   --------
          Mobil Oil Corporation                      51%        52%        54%
          Genesis Crude Oil, L.P.                    26%        27%        27%
          Western Gas Resources, Inc.                19%        15%        10%

       The  above  customers  represent  78% of  total  accounts  receivable  at
December 31, 1997.

       Pioneer USA is party  to a long-term agreement  pursuant to which Pioneer
USA and affiliates are to sell to Basis Petroleum, Inc. (formerly Phibro Energy,

                                       20

<PAGE>



Inc.)  substantially  all crude  oil  (including  condensate)  which any of such
entities  have the right to market  from time to time.  On  November  25,  1996,
Pioneer USA  consented to the  assignment of the agreement to Genesis Crude Oil,
L.P.  ("Genesis"),  a limited  partnership  formed by Basis Petroleum,  Inc. and
Howell Corporation.  The price to be paid by Genesis for oil purchased under the
agreement  ("Genesis Agreement")  is to be competitive with prices paid by other
substantial  purchasers  in the same areas who are  significant  competitors  of
Genesis.  The price to be paid for oil  purchased  under the  Genesis  Agreement
includes a  market-related  bonus  that may vary from month to month  based upon
spot oil prices at  various  commodity  trade  points.  The term of the  Genesis
Agreement is through June 30, 1998,  and it may continue  thereafter  subject to
termination  rights  afforded each party.  Salomon,  Inc., the parent company of
Basis Petroleum, Inc. and a subordinated limited partner in Genesis, secures the
payment  obligations  under the Genesis  Agreement  with a $25  million  payment
guarantee.  Accounts  receivable-oil  and gas sales  included  $18,739  due from
Genesis at December 31, 1997.

Note 9.     Organization and operations

       The Partnership was organized December 31, 1991 as a limited  partnership
under the Delaware Act for the purpose of acquiring and  developing  oil and gas
properties.  The general partners were converted to limited partners on November
30, 1992. The managing  general partner  received an opinion of legal counsel to
the  effect  that such  conversion  will not  result  in  material  adverse  tax
consequences.  The  following  is  a  brief  summary  of  the  more  significant
provisions of the limited partnership agreement:

       Managing   general  partner  -  The  managing   general  partner  of  the
       Partnership  is Pioneer USA.  Pioneer USA has the power and  authority to
       manage, control and administer all Partnership affairs. Under the limited
       partnership  agreement,  the  managing  general  partner  pays  1% of the
       Partnership's  acquisition,  drilling and completion costs, and 1% of its
       operating  and  general  and  administrative  expenses.  In  return it is
       allocated 1% of the Partnership's revenues.

       Limited  partner  liability  - The  maximum  amount of  liability  of any
       limited partner is the total contributions of such partner plus his share
       of any undistributed profits.

       Initial  capital  contributions  -  The  limited  partners  entered  into
       subscription   agreements   for  aggregate   capital   contributions   of
       $11,249,000.  The  managing  general  partner is required  to  contribute
       amounts equal to 1% of initial  Partnership capital less sales commission
       costs  allocated  to  the  limited  partners  and to  contribute  amounts
       necessary to pay costs and expenses allocated to it under the Partnership
       agreement to the extent its share of revenues does not cover such costs.

                                       21

<PAGE>



ITEM 9.     Changes in and Disagreements with Accountants on Accounting
              and Financial Disclosure

None


                                       22

<PAGE>



                                    PART III

ITEM 10.     Directors and Executive Officers of the Partnership

The  Partnership  does not have any  officers  or  directors.  Under the limited
partnership agreement,  the Partnership's managing general partner, Pioneer USA,
is  granted  the  exclusive  right and full  authority  to manage,  control  and
administer the Partnership's business.  Pioneer USA is a wholly-owned subsidiary
of Pioneer, a publicly-traded corporation on the New York Stock Exchange.

Set forth below are the names, ages and positions of the directors and executive
officers of Pioneer USA. Directors of Pioneer USA are elected to serve until the
next annual meeting of  stockholders  or until their  successors are elected and
qualified.
                            Age at
                         December 31,
        Name                 1997                       Position
--------------------     ------------     -------------------------------------
Scott D. Sheffield            45          President and Director

Timothy L. Dove               41          Executive Vice President and Director

Dennis E. Fagerstone          48          Executive Vice President and Director

Mark L. Withrow               50          Executive Vice President, General
                                            Counsel and Director

M. Garrett Smith              36          Executive Vice President, Chief
                                            Financial Officer and Director

Mel Fischer                   63          Executive Vice President

Lon C. Kile                   42          Executive Vice President

Rich Dealy                    31          Vice President and Chief Accounting
                                            Officer

     Scott D.  Sheffield.  Mr.  Sheffield  is a  distinguished  graduate  of The
University of Texas with a B.S. in Petroleum Engineering.  Since August 1997, he
has served as President,  Chief Executive  Officer and a director of Pioneer and
President  and a director of Pioneer USA. Mr.  Sheffield was the President and a
director  of  Parker  &  Parsley  from May 1990  until  August  1997 and was the
Chairman  of the Board  and Chief  Executive  Officer  of Parker & Parsley  from
October  1990 until August  1997.  He was the sole  director of Parker & Parsley
from  May 1990  until  October  1990.  Mr.  Sheffield  joined  Parker &  Parsley
Development Company ("PPDC"),  a predecessor of Parker & Parsley, as a petroleum
engineer  in 1979.  He  served  as Vice  President  -  Engineering  of PPDC from
September 1981 until April 1985 when he was elected President and a director. In
March 1989, Mr.  Sheffield was elected Chairman of the Board and Chief Executive
Officer of PPDC. Before joining PPDC, Mr. Sheffield was employed as a production
and reservoir engineer for Amoco Production Company.

                                       23

<PAGE>


     Timothy L. Dove.  Mr.  Dove  became  Executive  Vice  President  - Business
Development  of Pioneer and Pioneer USA in August 1997. He was also  appointed a
director of Pioneer USA in August 1997.  Mr. Dove joined Parker & Parsley in May
1994 as Vice President - International and was promoted to Senior Vice President
- Business Development in October 1996, in which position he served until August
1997.  Prior to joining  Parker & Parsley,  Mr. Dove was  employed  with Diamond
Shamrock Corp., and its successor,  Maxus Energy Corp, in various  capacities in
international exploration and production,  marketing, refining and marketing and
planning and development.  Mr. Dove earned a B.S. in Mechanical Engineering from
Massachusetts  Institute of Technology  in 1979 and received his M.B.A.  in 1981
from the University of Chicago.

     Dennis E. Fagerstone.  Mr. Fagerstone, a graduate of the Colorado School of
Mines with a B.S. in Petroleum  Engineering,  became an Executive Vice President
of Pioneer and Pioneer USA in August 1997.  He was also  appointed a director of
Pioneer USA in August 1997.  He served as  Executive  Vice  President  and Chief
Operating  Officer of Mesa from March 1, 1997 until  August  1997.  From October
1996 to February 1997, Mr.  Fagerstone served as Senior Vice President and Chief
Operating  Officer of Mesa and from May 1991 to October  1996, he served as Vice
President - Exploration  and Production of Mesa. From June 1988 to May 1991, Mr.
Fagerstone served as Vice President - Operations of Mesa.

     Mark L. Withrow.  Mr. Withrow,  a graduate of Abilene Christian  University
with a B. S. in  Accounting  and Texas Tech  University  with a Juris  Doctorate
degree,  became  Executive  Vice  President,  General  Counsel and  Secretary of
Pioneer  and  Pioneer USA in August  1997.  He was also  appointed a director of
Pioneer USA in August 1997. Mr. Withrow was Vice President - General  Counsel of
Parker & Parsley from January 1991, when he joined Parker & Parsley,  to January
1995,  when he was appointed  Senior Vice  President - General  Counsel.  He was
Parker &  Parsley's  Secretary  from  August 1992 until  August  1997.  Prior to
joining Parker & Parsley,  Mr. Withrow was the managing  partner of the law firm
of Turpin, Smith, Dyer, Saxe & MacDonald, Midland, Texas.

     M. Garrett  Smith.  Mr. Smith, a graduate of The University of Texas with a
B.S. in Electrical Engineering and Southern Methodist University with an M.B.A.,
was appointed Executive Vice President and Chief Financial Officer of Pioneer in
December  1997.  He served as Senior Vice  President  - Finance of Pioneer  from
August 1997 until  December  1997. Mr. Smith was elected Senior Vice President -
Finance  and a  director  of  Pioneer  USA in  August  1997.  He  served as Vice
President - Corporate  Acquisitions of Mesa from January 1997 until August 1997.
From October 1996 to December 1996, Mr. Smith served as Vice President - Finance
of Mesa and from 1994 to 1996 he served as  Director  of  Financial  Planning of
Mesa. Mr. Smith was employed by BTC Partners,  Inc. (a former financial  advisor
to Mesa) from 1989 to 1994.

     Mel Fischer.  Mr.  Fischer,  a graduate of the  University of California at
Berkeley with a Masters  degree in Geology,  became  Executive  Vice President -
Worldwide  Exploration of Pioneer and Pioneer USA in August 1997. He served as a
director  of Parker & Parsley  from  November  1995  until  August  1997 and was
Executive  Vice  President -  Worldwide  Exploration  for Parker & Parsley  from
February 1997 to August 1997. Mr.  Fischer worked in the petroleum  industry for
32 years, starting as a Petroleum Geologist with Texaco in 1962, and retiring as
President,  Occidental International Exploration and Production Company in March

                                       24

<PAGE>


1994. For the 10 years prior to becoming President of Occidental  International,
he served as Executive Vice President,  World Wide  Exploration  with Occidental
Oil  and  Gas  Corporation.   He  is  a  registered  geologist  in the  State of
California,  a member of the American Association of Petroleum Geologists and an
emeritus  member  of the  Board of  Advisors  for the  Earth  Sciences  Research
Institute at the University of Utah.

     Lon C. Kile.  Mr.  Kile,  a graduate of Oklahoma  State  University  with a
B.B.A. in Accounting, became Executive Vice President of Pioneer and Pioneer USA
in August 1997.  Mr. Kile was Senior Vice  President - Investor  Relations  from
October 1996 to August 1997. Previously, he served as Vice President and Manager
of the  Mid-Continent  Division,  Vice President - Equity Finance & Analysis and
Vice President - Marketing & Program  Administration.  Prior to joining Parker &
Parsley in 1985,  he was employed as  Supervisor - Senior,  Audit,  in charge of
Parker & Parsley's audit, with Ernst & Young.

     Rich Dealy. Mr. Dealy is a graduate of Eastern New Mexico University with a
B.B.A. in Accounting and Finance and is a Certified Public Accountant. He became
Vice  President  and Chief  Accounting  Officer of Pioneer  and  Pioneer  USA in
February 1998. Mr. Dealy served as Controller of Pioneer USA from August 1997 to
February  1998.  He served as Controller of Parker & Parsley from August 1995 to
August 1997. Mr. Dealy joined Parker & Parsley as an Accounting Manager in July,
1992. He was previously  employed with KPMG Peat Marwick as an Audit Senior,  in
charge of Parker & Parsley's audit.

ITEM 11.     Executive Compensation

The  Partnership  does not have any  directors  or officers.  Management  of the
Partnership  is  vested  in  the  managing  general  partner.   The  Partnership
participates in oil and gas activities  through an income tax  partnership  (the
"Program")  pursuant to the  Program  agreement.  Under the  Program  agreement,
Pioneer USA and P&P  Employees  91-B GP ("EMPL")  pay  approximately  25% of the
Partnership's  acquisition,  drilling and completion costs and approximately 35%
of its operating and general and administrative  expenses.  In return,  they are
allocated  approximately 35% of the Partnership's revenues. See Notes 6 and 9 of
Notes to Financial  Statements  included in "Item 8.  Financial  Statements  and
Supplementary  Data" for information  regarding fees and reimbursements  paid to
the managing general partner or its affiliates by the Partnership.

Pioneer  USA's  current  executive  officers  and other  employees  are  general
partners of EMPL. EMPL serves as a co-general partner of the Program. Under this
arrangement,  EMPL pays  approximately  2.5% of the  Partnership's  acquisition,
drilling  and  completion  costs and  approximately  3.5% of its  operating  and
general and administrative  expenses. In return, EMPL is allocated approximately
3.5%  of  the  Partnership's  revenues.  EMPL  does  not  receive  any  fees  or
reimbursements from the Partnership.

The Partnership does not directly pay any salaries of the executive  officers or
employees of Pioneer USA,  but does pay a portion of Pioneer  USA's  general and
administrative  expenses of which these salaries are a part. See Note 6 of Notes
to  Financial   Statements  included  in  "Item  8.  Financial   Statements  and
Supplementary Data".

                                       25

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ITEM 12.     Security Ownership of Certain Beneficial Owners and Management

(a)      Beneficial owners of more than five percent

The Partnership is not aware of any person who  beneficially  owns 5% or more of
the outstanding  limited partnership  interests of the Partnership.  Pioneer USA
owned 10 limited partner interests at January 1, 1998.

(b)      Security ownership of management

The Partnership  does not have any officers or directors.  The managing  general
partner  of the  Partnership,  Pioneer  USA,  has the  exclusive  right and full
authority to manage,  control and administer the Partnership's  business.  Under
the limited  partnership  agreement,  limited partners holding a majority of the
outstanding  limited  partnership  interests  have  the  right  to take  certain
actions,  including  the removal of the  managing  general  partner or any other
general  partner.  The  Partnership  is not aware of any current  arrangement or
activity  which may lead to such removal.  The  Partnership  is not aware of any
officer or director of Pioneer USA who  beneficially  owns  limited  partnership
interests in the Partnership.

ITEM 13.     Certain Relationships and Related Transactions

Transactions with the managing general partner or its affiliates

Pursuant to the limited partnership agreement, the Partnership had the following
related party  transactions  with the managing general partner or its affiliates
during the years ended December 31:
                                                    1997       1996       1995
                                                  --------   --------   --------
 Payment of lease operating and supervision
    charges in accordance with standard industry
    operating agreements                          $194,622   $176,738   $158,487

 Reimbursement of general and administrative
    expenses                                      $ 35,160   $ 31,806   $ 31,570

 Receipt of proceeds for the salvage value of
    retired oil and gas equipment                 $    -     $    412   $    -

 Purchase of oil and gas properties and related
    equipment, at predecessor cost                $  1,623   $    -     $ 16,310

Under the limited partnership agreement, the managing general partner pays 1% of
the  Partnership's  acquisition,  drilling  and  completion  costs and 1% of its
operating and general and administrative expenses. In return, it is allocated 1%
of the  Partnership's  revenues.  Also,  see Notes 6 and 9 of Notes to Financial
Statements  included in "Item 8. Financial  Statements and Supplementary  Data",
regarding the Partnership's  participation  with the managing general partner in
oil and gas activities of the Program.

                                       26

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                                     PART IV


ITEM 14.     Exhibits, Financial Statement Schedules and Reports on Form 8-K.

(a)    1.     Financial statements

              The following are filed as part of this annual report:

                    Independent Auditors' Report

                    Balance sheets as of December 31, 1997 and 1996

                    Statements of operations for the years ended December 31,
                      1997, 1996 and 1995

                    Statements of partners' capital for the years ended December
                      31, 1997, 1996 and 1995

                    Statements of cash flows for the years ended December 31,
                      1997, 1996 and 1995

                    Notes to financial statements

       2.     Financial statement schedules

              All  financial  statement  schedules  have been omitted  since the
              required  information  is in the  financial  statements  or  notes
              thereto, or is not applicable nor required.

(b)    Reports on Form 8-K

       None.

(c)    Exhibits

       The exhibits  listed on the  accompanying  index to exhibits are filed or
       incorporated by reference as part of this annual report.

                                       27

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                               S I G N A T U R E S

       Pursuant to the requirements 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.

                                         PARKER & PARSLEY 91-B, L.P.

Dated: March 26, 1998            By:     Pioneer Natural Resources USA, Inc.
                                           Managing General Partner

                                         By:    /s/ Scott D. Sheffield
                                              ---------------------------------
                                                Scott D. Sheffield, President

       Pursuant to the requirements of the Securities Exchange Act of 1934, this
report  has  been  signed  below  by the  following  persons  on  behalf  of the
Registrant and in the capacities and on the date indicated.


/s/ Scott D. Sheffield     President and Director of            March 26, 1998
-------------------------  Pioneer USA
Scott D. Sheffield

/s/ Timothy L. Dove        Executive Vice President and         March 26, 1998
-------------------------  Director of Pioneer USA
Timothy L. Dove

/s/ Dennis E. Fagerstone   Executive Vice President and         March 26, 1998
-------------------------  Director of Pioneer USA
Dennis E. Fagerstone

/s/ Mark L. Withrow        Executive Vice President, General    March 26, 1998
-------------------------  Counsel and Director of Pioneer USA
Mark L. Withrow

/s/ M. Garrett Smith       Executive Vice President, Chief      March 26, 1998
-------------------------  Financial Officer and Director of
M. Garrett Smith           Pioneer USA

/s/ Mel Fischer            Executive Vice President of          March 26, 1998
-------------------------  Pioneer USA
Mel Fischer

/s/ Lon C. Kile            Executive Vice President of          March 26, 1998
-------------------------  Pioneer USA
Lon C. Kile

/s/ Rich Dealy             Vice President and Chief Accounting  March 26, 1998
-------------------------  Officer of Pioneer USA
Rich Dealy
                                       28

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                           PARKER & PARSLEY 91-B, L.P.

                                INDEX TO EXHIBITS

       The following documents are incorporated by reference in response to Item
14(c):

Exhibit No.                       Description                           Page
-----------                       -----------                           ----
    3(a)           Form of Agreement of Limited Partnership                -
                   of Parker & Parsley 91-B, L.P. incorporated
                   by reference to Exhibit A of the Partnership's
                   Registration Statement on Form S-1
                   (Registration No. 33-38582) (hereinafter
                   called the Partnership's Registration Statement)

    4(b)           Form of Limited Partner Subscription Agree-             -
                   ment incorporated by reference to Exhibit C of
                   the Partnership's Registration Statement

    4(b)           Form of General Partner Subscription Agree-             -
                   ment incorporated by reference to Exhibit D of
                   the Partnership's Registration Statement

    4(b)           Power of Attorney incorporated by reference to          -
                   Exhibit B of the Partnership's Registration
                   Statement

    4(c)           Specimen Certificate of Limited Partnership             -
                   Interest incorporated by reference to Exhibit 4.3
                   of Amendment No. 2 of the Partnership's
                   Registration Statement

   10(b)           Development Drilling Program Agreement                  -
                   incorporated by reference to Exhibit B of the
                   Partnership's Registration Statement

     27.1*         Financial Data Schedule

*Filed herewith
                                       29

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