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                                FORM 10-Q

                    SECURITIES AND EXCHANGE COMMISSION
                         WASHINGTON, D.C.  20549

(MARK ONE)

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

For the quarterly period ended March 31, 2005

                                    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 0-20298

         SOUTHWEST ROYALTIES INSTITUTIONAL 1990-91 INCOME PROGRAM
         Southwest Royalties Institutional Income Fund X-C, L.P.
                  (Exact name of registrant as specified
                  in its limited partnership agreement)

Delaware                                           75-2374449
(State or other jurisdiction of         (I.R.S. Employer
incorporation or organization)        Identification No.)


                         6 Desta Drive, Suite 6500
                           Midland, Texas 79705
                 (Address of principal executive offices)

                              (432) 682-6324
                      (Registrant's telephone number,
                           including area code)

Indicate  by  check  mark  whether 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 whether the registrant is an accelerated filer  (as
defined in Exchange Act Rule 12b-2).     Yes     No  X

The  registrant's  outstanding  securities  consist  of  Units  of  limited
partnership  interests for which there exists no established public  market
from which to base a calculation of aggregate market value.

        The total number of pages contained in this report is 21.

<PAGE>
Glossary of Oil and Gas Terms
The  following are abbreviations and definitions of terms commonly used  in
the  oil  and  gas industry that are used in this filing.  All  volumes  of
natural gas referred to herein are stated at the legal pressure base to the
state  or area where the reserves exit and at 60 degrees Fahrenheit and  in
most instances are rounded to the nearest major multiple.

     Bbl. One stock tank barrel, or 42 United States gallons liquid volume.

     BOE.   Equivalent  barrels of oil, with natural gas converted  to  oil
equivalents based on a ratio of six Mcf of natural gas to one Bbl of oil.

     Developmental well. A well drilled within the proved area of an oil or
natural gas reservoir to the depth of a stratigraphic horizon known  to  be
productive.

     Exploratory well. A well drilled to find and produce oil or gas in  an
unproved  area to find a new reservoir in a field previously  found  to  be
productive of oil or natural gas in another reservoir or to extend a  known
reservoir.

     Farm-out arrangement. An agreement whereby the owner of a leasehold or
working  interest agrees to assign his interest in certain specific acreage
to  an  assignee,  retaining some interest, such as an  overriding  royalty
interest,  subject  to  the drilling of one (1)  or  more  wells  or  other
specified performance by the assignee.

     Field. An area consisting of a single reservoir or multiple reservoirs
all  grouped  on  or  related to the same individual geological  structural
feature and/or stratigraphic condition.

     Mcf. One thousand cubic feet.

     Net  Profits  Interest.  An agreement whereby  the  owner  receives  a
specified  percentage of the defined net profits from a producing  property
in  exchange for consideration paid.  The net profits interest  owner  will
not otherwise participate in additional costs and expenses of the property.

     Oil. Crude oil, condensate and natural gas liquids.

     Overriding  royalty  interest. Interests that  are  carved  out  of  a
working  interest, and their duration is limited by the term of  the  lease
under which they are created.

<PAGE>

     Present  value  and  PV-10 Value. When used with respect  to  oil  and
natural gas reserves, the estimated future net revenue to be generated from
the  production of proved reserves, determined in all material respects  in
accordance  with  the  rules and regulations of the  SEC  (generally  using
prices  and costs in effect as of the date indicated) without giving effect
to  non-property  related  expenses  such  as  general  and  administrative
expenses,  debt service and future income tax expenses or to  depreciation,
depletion  and  amortization, discounted using an annual discount  rate  of
10%.

     Production  costs.  Costs incurred to operate and maintain  wells  and
related  equipment  and facilities, including depreciation  and  applicable
operating  costs  of support equipment and facilities and  other  costs  of
operating and maintaining those wells and related equipment and facilities.

     Proved Area. The part of a property to which proved reserves have been
specifically attributed.

     Proved  developed  oil and gas reserves. Proved oil and  gas  reserves
that  can  be  expected to be recovered from existing wells  with  existing
equipment and operating methods.

     Proved properties. Properties with proved reserves.

     Proved  oil  and gas reserves. The estimated quantities of crude  oil,
natural  gas, and natural gas liquids with geological and engineering  data
that  demonstrate  with  reasonable certainty to be recoverable  in  future
years   from  known  reservoirs  under  existing  economic  and   operating
conditions, i.e., prices and costs as of the date the estimate is made.

     Proved  undeveloped  reserves. Proved oil and gas  reserves  that  are
expected  to  be  recovered from new wells on undrilled  acreage,  or  from
existing  wells  where  a  relatively major  expenditure  is  required  for
recompletion.

     Reservoir.  A porous and permeable underground formation containing  a
natural  accumulation  of  producible  oil  or  gas  that  is  confined  by
impermeable  rock  or water barriers and is individual  and  separate  from
other reservoirs.

     Royalty  interest.  An  interest in an oil and  natural  gas  property
entitling  the  owner to a share of oil or natural gas production  free  of
costs of production.

     Working  interest.  The operating interest that gives  the  owner  the
right  to  drill, produce and conduct operating activities on the  property
and a share of production.

     Workover.  Operations  on  a producing well  to  restore  or  increase
production.

<PAGE>
                     PART I. - FINANCIAL INFORMATION


Item 1.   Financial Statements

The  unaudited  condensed financial statements included  herein  have  been
prepared  by  the Registrant (herein also referred to as the "Partnership")
in  accordance  with generally accepted accounting principles  for  interim
financial information and with the instructions to Form 10-Q and Rule 10-01
of Regulation S-X.  Accordingly, they do not include all of the information
and  footnotes  required  by generally accepted accounting  principles  for
complete   financial  statements.   In  the  opinion  of  management,   all
adjustments necessary for a fair presentation have been included and are of
a  normal  recurring nature.  The financial statements should  be  read  in
conjunction with the audited financial statements and the notes thereto for
the  year ended December 31, 2004, which are found in the Registrant's Form
10-K  Report  for  2004 filed with the Securities and Exchange  Commission.
The December 31, 2004 balance sheet included herein has been taken from the
Registrant's 2004 Form 10-K Report.  Operating results for the three  month
period  ended March 31, 2005 are not necessarily indicative of the  results
that may be expected for the full year.





<PAGE>
         Southwest Royalties Institutional Income Fund X-C, L.P.
                              Balance Sheets

                                  March    December
                                   31,       31,
                                   2005      2004
                                   ----      ----
                                 (unaudit
                                   ed)
Assets
----------

Current assets:
 Cash and cash equivalents    $  26,339    32,864
  Receivable  from  Managing     119,857   107,812
General Partner
                                 --------  --------
                                 ----      ----
   Total current assets          146,196   140,676
                                 --------  --------
                                 ----      ----
Oil  and  gas  properties  -
using the full-
 method of accounting            2,395,60  2,395,60
                                 1         1
       Less      accumulated
depreciation,
         depletion       and     2,240,27  2,238,61
amortization                     4         4
                                 --------  --------
                                 ----      ----
      Net   oil   and    gas     155,327   156,987
properties
                                 --------  --------
                                 ----      ----
                              $  301,523   297,663
                                 =======   =======
Liabilities  and   Partners'
Equity
----------------------------
-----------

Current liability:
  Distribution payable        $  360       262
                                 --------  --------
                                 ----      ----

Asset retirement obligation      808,609   798,702
                                 --------  --------
                                 ----      ----

Partners' (deficit):
 General partners                (91,697)  (91,248)
 Limited partners                (415,749  (410,053
                                 )         )
                                 --------  --------
                                 ----      ----
   Total partners' (deficit)     (507,446  (501,301
                                 )         )
                                 --------  --------
                                 ----      ----
                              $  301,523   297,663
                                 =======   =======











                  The accompanying notes are an integral
                    part of these financial statements.
<PAGE>
         Southwest Royalties Institutional Income Fund X-C, L.P.
                         Statements of Operations
                               (unaudited)

                                        Three Months Ended
                                            March 31,
                                         2005        2004
                                         ----        ----
Revenues
-------------
    Income   from   net   profits  $  118,262     91,227
interests
 Interest                             135         43
 Other                                -           250
                                      ----------  ---------
                                                  -
                                      118,397     91,520
                                      ----------  ---------
                                                  -
Expenses
------------
 General and administrative           12,975      12,569
   Depreciation,  depletion   and     1,660       3,000
amortization
  Accretion  of asset  retirement     9,907       14,817
obligation
                                      ----------  ---------
                                                  -
                                      24,542      30,386
                                      ----------  ---------
                                                  -
Net    income   from    continued     93,855      61,134
operations

Results     from     discontinued
operations -
 sale of oil and gas leases - See     -           (4,607)
Note 3
                                      ----------  ---------
                                                  -
Net income                         $  93,855      56,527
                                      ======      ======
Net income allocated to:

 Managing General Partner          $  8,596       5,357
                                      ======      ======
 General partner                   $  955         596
                                      ======      ======
 Limited partners                  $  84,304      50,574
                                      ======      ======
     Per   limited  partner  unit
before discontinued
     operations  and   cumulative  $   14.09           9.15
effect
    Discontinued  operations  per          -
limited partner unit                              (.69)
                                      ----------  ---------
                                                  -
  Per limited partner unit         $   14.09           8.46
                                      ======      ======










                  The accompanying notes are an integral
                    part of these financial statements.
<PAGE>
         Southwest Royalties Institutional Income Fund X-C, L.P.

                         Statements of Cash Flows
                               (unaudited)

                                      Three Months Ended
                                           March 31,
                                        2005       2004
                                       -----       ----
Cash    flows   from    operating
activities:

  Cash  received from net profits  $ 106,217    44,506
interest
 Cash paid to suppliers              (12,975)   (12,569)
 Discontinued operations             -          (4,607)
 Interest received                   135        43
 Other                               -          250
                                     ---------  ---------
                                     -          -
   Net cash provided by operating    93,377     27,623
activities
                                     ---------  ---------
                                     -          -
Cash    flows   from    financing
activities:

 Distributions to partners           (100,000)  (30,000)
 Increase in distribution payable    98         -
                                     ---------  ---------
                                     -          -
   Net  cash  used  in  financing    (99,902)   (30,000)
activities
                                     ---------  ---------
                                     -          -
Net  decrease  in cash  and  cash    (6,525)    (2,377)
equivalents

 Beginning of period                 32,864     26,631
                                     ---------  ---------
                                     -          -
 End of period                     $ 26,339     24,254
                                     ======     ======
Reconciliation of net  income  to
net cash
     provided     by    operating
activities:

Net income                         $ 93,855     56,527

Adjustments   to  reconcile   net
income to
  net  cash provided by operating
activities:

   Depreciation,  depletion   and    1,660      3,000
amortization
  Accretion  of asset  retirement    9,907      14,817
obligation
 Increase in receivables             (12,045)   (46,721)
 Increase in payables                -          -
                                     ---------  ---------
                                     -          -
Net  cash  provided by  operating  $ 93,377     27,623
activities
                                     ======     ======








                  The accompanying notes are an integral
                    part of these financial statements.
<PAGE>
         Southwest Royalties Institutional Income Fund X-C, L.P.
                     (a Delaware limited partnership)

                      Notes to Financial Statements

1.   Organization
     Southwest  Royalties Institutional Income Fund X-C, L.P. was organized
     under the laws of the state of Delaware on September 20, 1991, for the
     purpose  of acquiring producing oil and gas properties and to  produce
     and market crude oil and natural gas produced from such properties for
     a  term  of 50 years, unless terminated at an earlier date as provided
     for  in the Partnership Agreement.  The Partnership sells its oil  and
     gas production to several purchasers with the prices it receives being
     dependent upon the oil and gas economy.  Southwest Royalties, Inc.,  a
     wholly  owned subsidiary of Clayton Williams Energy, Inc.,  serves  as
     the  Managing  General  Partner.  Revenues,  costs  and  expenses  are
     allocated as follows:

                         Limited   General
                         Partners  Partners
                         --------  --------
Interest   income    on    100%       -
capital contributions
Oil and gas sales          90%       10%
All other revenues         90%       10%
Organization        and    100%       -
offering costs (1)
Syndication costs          100%       -
Amortization         of    100%       -
organization costs
Property    acquisition    100%       -
costs
Gain/loss  on  property    90%       10%
disposition
Operating           and    90%       10%
administrative    costs
(2)
Depreciation, depletion
and amortization
   of   oil   and   gas    100%       -
properties
All other costs            90%       10%

          (1)   All  organization costs in excess of 3% of initial  capital
          contributions  will be paid by the Managing General  Partner  and
          will  be treated as a capital contribution.  The Partnership paid
          the  Managing  General Partner an amount equal to 3%  of  initial
          capital contributions for such organization costs.

          (2)  Administrative costs in any year, which exceed 2% of capital
          contributions shall be paid by the Managing General  Partner  and
          will be treated as a capital contribution.

2.   Summary of Significant Accounting Policies
     The  interim financial information as of March 31, 2005, and  for  the
     three  months ended March 31, 2005, is unaudited.  Certain information
     and  footnote  disclosures normally included in  financial  statements
     prepared  in accordance with generally accepted accounting  principles
     have been condensed or omitted in this Form 10-Q pursuant to the rules
     and  regulations of the Securities and Exchange Commission.   However,
     in  the  opinion  of  management, these interim  financial  statements
     include all the necessary adjustments to fairly present the results of
     the interim periods and all such adjustments are of a normal recurring
     nature.  The interim consolidated financial statements should be  read
     in  conjunction with the Partnership's Annual Report on Form 10-K  for
     the year ended December 31, 2004.

     In September 2004, the Securities and Exchange Commission issued Staff
     Accounting  Bulletin No. 106 ("SAB 106"). SAB 106  expresses  the  SEC
     staff's views regarding SFAS No. 143 and its impact on both the  full-
     cost  ceiling  test  and  the calculation of  depletion  expense.   In
     accordance  with  SAB  106, beginning in the first  quarter  of  2005,
     undiscounted abandonment costs for wells to be drilled in  the  future
     to develop proved reserves are included in the unamortized cost of oil
     and  gas  properties, net of related salvage value,  for  purposes  of
     computing  depreciation,  depletion  and  amortization  ("DD&A").  The
     implementation  of  SAB  106 did not have a  material  impact  on  our
     financial statements.

<PAGE>
         Southwest Royalties Institutional Income Fund X-C, L.P.
                     (a Delaware limited partnership)

                      Notes to Financial Statements


3.   Discontinued Operations - Sale of oil and gas leases
     During 2003, the Partnership sold its interest in certain oil and  gas
     wells  for  $81,184  sales  proceeds and  retired  $100,007  of  asset
     retirement  obligation  associated with  the  properties.   Since  the
     Partnership  is  under the full cost pool method  of  accounting,  the
     sales  proceeds and asset retirement obligation liability  were  taken
     against  the  oil and gas properties asset account and  therefore,  no
     gain or loss was recorded and shown on the statement of operations  as
     part  of  the  discontinued operations. Operating  expenses  for  2004
     represent  plugging  and abandonment costs that  the  Partnership  was
     contractually committed to perform prior to the sale of the  property.
     Plugging  and abandonment services were performed during  the  quarter
     ended  March 31, 2004.  Pursuant to the requirements of SFAS No.  144,
     the  operating  results from these properties have  been  reported  as
     discontinued operations in the accompanying statements of operations.

     The   following   table   summarizes  certain   historical   operating
     information related to the discontinued operations:

                  Three
                  months end
                  March 31,
                     2004

Income from net
profit
   interest       $(4,607)


<PAGE>
Item 2.   Management's  Discussion and Analysis of Financial Condition  and
          Results of Operations

General

Southwest Royalties Institutional Income Fund X-C, L.P. was organized as  a
Delaware limited partnership on September 20, 1991.  The offering  of  such
limited  partnership interests began October 1, 1991 as  part  of  a  shelf
offering registered under the name Southwest Royalties Institutional  1990-
91  Income Program.  Minimum capital requirements for the Partnership  were
met on January 28, 1992, with the offering of limited partnership interests
concluding April 30, 1992.

The Partnership was formed to acquire royalty and net profits interests  in
producing  oil  and  gas properties, to produce and market  crude  oil  and
natural  gas  produced  from such properties, and  to  distribute  the  net
proceeds from operations to the limited and general partners.  Net revenues
from  producing  oil  and gas properties will not be  reinvested  in  other
revenue  producing  assets except to the extent that production  facilities
and wells are improved or reworked or where methods are employed to improve
or  enable  more efficient recovery of oil and gas reserves.  The  economic
life  of  the  Partnership  thus  depends on  the  period  over  which  the
Partnership's oil and gas reserves are economically recoverable.

Increases   or   decreases   in  Partnership   revenues   and,   therefore,
distributions  to partners will depend primarily on changes in  the  prices
received  for  production,  changes in volumes of  production  sold,  lease
operating  expenses, enhanced recovery projects, offset drilling activities
pursuant  to farm-out arrangements, sales of properties, and the  depletion
of  wells.   Since  wells deplete over time, production  can  generally  be
expected to decline from year to year.

Well  operating costs and general and administrative costs usually decrease
with   production   declines;  however,  these  costs  may   not   decrease
proportionately.  Net income available for distribution to the partners  is
therefore expected to decline in later years based on these factors.

Oil and Gas Properties

Oil  and  gas  properties  are accounted for at cost  under  the  full-cost
method.  Under this method, all productive and nonproductive costs incurred
in  connection with the acquisition, exploration and development of oil and
gas  reserves  are capitalized.  Gain or loss on the sale of  oil  and  gas
properties  is not recognized unless significant oil and gas  reserves  are
sold.

Should the net capitalized costs exceed the estimated present value of  oil
and gas reserves, discounted at 10%, such excess costs would be charged  to
current  expense. As of March 31, 2005, the net capitalized costs  did  not
exceed the estimated present value of oil and gas reserves.


<PAGE>
The  Partnership's  interest  in oil and gas  properties  consists  of  net
profits  interests  in  proved properties located  within  the  continental
United  States.   A net profits interest is created when  the  owner  of  a
working  interest in a property enters into an arrangement  providing  that
the  net profits interest owner will receive a stated percentage of the net
profit  from  the  property.   The  net profits  interest  owner  will  not
otherwise participate in additional costs and expenses of the property.

The  Partnership recognizes income from its net profits interest in oil and
gas property on an accrual basis, while the quarterly cash distributions of
the net profits interest are based on a calculation of actual cash received
from  oil  and  gas sales, net of expenses incurred during  that  quarterly
period.  If  the  net  profits  interest calculation  results  in  expenses
incurred  exceeding the oil and gas income received during  a  quarter,  no
cash  distribution is due to the Partnership's net profits  interest  until
the  deficit is recovered from future net profits.  The Partnership accrues
a quarterly loss on its net profits interest provided there is a cumulative
net  amount  due for accrued revenue as of the balance sheet date.   As  of
March  31,  2005,  there were no timing differences, which  resulted  in  a
deficit net profit interest.

Critical Accounting Policies

The  Partnership follows the full cost method of accounting for its oil and
gas  properties.   The  full cost method subjects  companies  to  quarterly
calculations of a "ceiling", or limitation on the amount of properties that
can  be capitalized on the balance sheet.  If the Partnership's capitalized
costs  are in excess of the calculated ceiling, the excess must be  written
off as an expense.

The  Partnership's discounted present value of its proved oil  and  natural
gas  reserves  is  a  major  component  of  the  ceiling  calculation,  and
represents  the  component  that requires the  most  subjective  judgments.
Estimates  of  reserves are forecasts based on engineering data,  projected
future  rates  of  production and the timing of future  expenditures.   The
process  of  estimating oil and natural gas reserves  requires  substantial
judgment,  resulting  in  imprecise determinations,  particularly  for  new
discoveries.   Different reserve engineers may make different estimates  of
reserve  quantities  based  on the same data.   The  Partnership's  reserve
estimates are prepared by outside consultants.

The  passage  of  time  provides  more  qualitative  information  regarding
estimates of reserves, and revisions are made to prior estimates to reflect
updated  information.   However,  there  can  be  no  assurance  that  more
significant  revisions  will not be necessary in  the  future.   If  future
significant  revisions  are  necessary  that  reduce  previously  estimated
reserve quantities, it could result in a full cost property writedown.   In
addition to the impact of these estimates of proved reserves on calculation
of  the  ceiling,  estimates  of proved reserves  are  also  a  significant
component  of  the calculation of depletion, depreciation, and amortization
("DD&A").

While  the quantities of proved reserves require substantial judgment,  the
associated prices of oil and natural gas reserves that are included in  the
discounted  present  value of the reserves do not  require  judgment.   The
ceiling calculation dictates that prices and costs in effect as of the last
day  of  the  period are generally held constant indefinitely. Because  the
ceiling  calculation dictates that prices in effect as of the last  day  of
the  applicable quarter are held constant indefinitely, the resulting value
is  not indicative of the true fair value of the reserves.  Oil and natural
gas  prices have historically been cyclical and, on any particular  day  at
the  end of a quarter, can be either substantially higher or lower than the
Partnership's  long-term price forecast that is a barometer for  true  fair
value.


<PAGE>
Results of Operations

General Comparison of the Quarters Ended March 31, 2005 and 2004

The  following  table  provides certain information  regarding  performance
factors for the quarters ended March 31, 2005 and 2004.

                               Three Months
                                  Ended         Percenta
                                                   ge
                                March 31,       Increase
                              2005      2004    (Decreas
                                                   e)
                             -----     -----    --------
                                                   --
Oil    production    in     5,670     5,710     (1%)
barrels
Gas production in mcf       2,361     5,800     (59%)
Total BOE                   6,064     6,677     (9%)
Average    price    per  $   47.73              54%
barrel of oil                         31.03
Average  price per  mcf  $    4.01              (12%)
of gas                                4.56
Income from net profits  $  118,262   91,227    30%
interests
Partnership              $  100,000   30,000    233%
distributions
Limited         partner  $  90,000    27,000    233%
distributions
Per  unit  distribution
to limited
 partners                $   15.04              233%
                                      4.51

Number    of    limited     5,983     5,983
partner units

Income from net profits

The  Partnership's income from net profits interests increased to  $118,262
from  $91,227 for the quarters ended March 31, 2005 and 2004, respectively,
an  increase of 30%. The principal factors affecting the comparison of  the
quarters ended March 31, 2005 and 2004 are as follows:

The average price for a barrel of oil received by the Partnership increased
during  the  quarter ended March 31, 2005 as compared to the quarter  ended
March  31,  2004 by 54%, or $16.69 per barrel, resulting in an increase  of
approximately  $94,700  in income from net profits  interests.   Oil  sales
represented  97% of total oil and gas sales during the quarter ended  March
31, 2005 as compared to 87% during the quarter ended March 31, 2004.

The  average price for an mcf of gas received by the Partnership  decreased
during the same period by 12%, or $.56 per mcf, resulting in a decrease  of
approximately $1,300 in income from net profits interests.

The  net  total increase in income from net profits interests  due  to  the
change  in  prices  received from oil and gas production  is  approximately
$93,400.  The market price for oil and gas has been extremely volatile over
the  past decade, and management expects a certain amount of volatility  to
continue in the foreseeable future.

<PAGE>
Oil  production decreased approximately 40 barrels or 1% during the quarter
ended  March  31,  2005 as compared to the quarter ended  March  31,  2004,
resulting in a decrease of approximately $1,200 in income from net  profits
interests.

Gas  production  decreased approximately 3,439 mcf or 59% during  the  same
period, resulting in a decrease of approximately $15,700 in income from net
profits interests.

The  total decrease in income from net profits interests due to the  change
in  production is approximately $16,900.   The decrease in gas  volumes  is
from a gas well with lower production due to down hole problems.

Lease   operating  costs  and  production  taxes  were   44%   higher,   or
approximately  $49,400  more during the quarter ended  March  31,  2005  as
compared  to  the  quarter ended March 31, 2004.   The  increase  in  lease
operating  costs is from increases in well repairs and production equipment
repairs on two properties.

Costs and Expenses

Total  costs and expenses decreased to $24,542 for the quarter ended  March
31,  2005  from  $30,386  for the same period in 2004.  This  represents  a
decrease  of  19%.   The decrease is the result of lower depletion  expense
and  accretion  expense,  partially offset by an increase  in  general  and
administrative expense.

General  and  administrative  costs consist of independent  accounting  and
engineering fees, computer services, postage, and Managing General  Partner
personnel  costs.   General  and  administrative  costs  increased  3%   or
approximately $400 during the quarter ended March 31, 2005 as  compared  to
the quarter ended March 31, 2004.

Depletion expense decreased to $1,660 for the quarter ended March 31,  2005
from $3,000 for the same period in 2004. This represents a decrease of 45%.
The contributing factor to the decrease in depletion expense is in relation
to  the BOE depletion rate for the quarter ended March 31, 2005, which  was
$.27 applied to 6,064 BOE as compared to $.45 applied to 6,677 BOE for  the
same period in 2004.  The lower depletion rate in 2005 is due to the upward
revision in reserve estimates resulting from higher oil and gas prices.

Accretion expense decreased to $9,907 for the quarter ended March 31,  2005
from  $14,817 for the same period in 2004.  This represents a  decrease  of
33%.  The decrease in accretion is from discontinuing accretion on  several
wells that reached their projected end of life in 2004.



<PAGE>
Liquidity and Capital Resources

The  primary source of cash is from operations, the receipt of income  from
interests in oil and gas properties.  The Partnership knows of no  material
change, nor does it anticipate any such change.

Cash  flows provided by operating activities were approximately $93,400  in
the  quarter ended March 31, 2005 as compared to approximately  $27,600  in
the quarter ended March 31, 2004.

Cash  flows used in financing activities were approximately $99,900 in  the
quarter  ended March 31, 2005 as compared to approximately $30,000  in  the
quarter ended March 31, 2004.  The only use in financing activities was the
distributions to partners.

Total  distributions during the quarter ended March 31, 2005 were  $100,000
of  which $90,000 ($15.04 per unit) was distributed to the limited partners
and  $10,000  to  the  general partners.  Total  distributions  during  the
quarter ended March 31, 2004 were $30,000 of which $27,000 ($4.51 per unit)
was distributed to the limited partners and $3,000 to the general partners.

The primary sources for the 2005 distributions of $100,000 were oil and gas
operations  of approximately $93,400, with the balance from available  cash
on  hand  at the beginning of the period. The primary sources for the  2004
distributions  of  $30,000  were oil and gas  operations  of  approximately
$27,600,  with the balance from available cash on hand at the beginning  of
the period.

Cumulative  cash distributions of $3,784,061 have been made to the  general
and  limited  partners.  As of March 31, 2005, $3,423,142  or  $572.14  per
limited  partner  unit  has  been  distributed  to  the  limited  partners,
representing a 114% return of the capital contributed.

As of March 31, 2005, the Partnership had approximately $145,800 in working
capital.   The  Managing  General Partner knows of no  unusual  contractual
commitments.  Although the partnership held many long-lived  properties  at
inception,  because of the restrictions on property development imposed  by
the partnership agreement, the Partnership cannot develop its non-producing
properties, if any.  Without continued development, the producing  reserves
continue  to  deplete.  Accordingly, as the Partnership's  properties  have
matured  and  depleted,  the  net  cash  flows  from  operations  for   the
partnership  has  steadily  declined, except in  periods  of  substantially
increased  commodity pricing.  Maintenance of properties and administrative
expenses for the Partnership are increasing relative to production.  As the
properties   continue   to   deplete,   maintenance   of   properties   and
administrative costs as a percentage of production are expected to continue
to increase.

<PAGE>
Recent Accounting Pronouncements

In  December 2004, the Financial Accounting Standards Board ("FASB") issued
Statement   of  Financial  Accounting  Standards  No.  153  "Exchanges   of
Nonmonetary  Assets,  an amendment of APB Opinion  No.  29"  ("SFAS  153").
SFAS  153  specifies  the criteria required to record a  nonmonetary  asset
exchange  using  carryover  basis.  SFAS 153 is effective  for  nonmonetary
asset  exchanges occurring after July 1, 2005.  The Partnership will  adopt
this statement in the third quarter of 2005, and it is not expected to have
a material effect on the financial statements when adopted.

In  September  2004,  the Securities and Exchange Commission  issued  Staff
Accounting Bulletin No. 106 ("SAB 106"). SAB 106 expresses the SEC  staff's
views  regarding SFAS No. 143 and its impact on both the full-cost  ceiling
test and the calculation of depletion expense.  In accordance with SAB 106,
beginning in the first quarter of 2005, undiscounted abandonment costs  for
wells  to  be drilled in the future to develop proved reserves are included
in  the  unamortized cost of oil and gas properties, net of related salvage
value,  for  purposes of computing depreciation, depletion and amortization
("DD&A").  The implementation of SAB 106 did not have a material impact  on
our financial statements.


<PAGE>
Item 3.   Quantitative and Qualitative Disclosures About Market Risk

The  Partnership  is  not a party to any derivative or embedded  derivative
instruments.

Item 4.   Controls and Procedures
The  Managing  General  Partner  has established  disclosure  controls  and
procedures   that  are  adequate  to  provide  reasonable  assurance   that
management will be able to collect, process and disclose both financial and
non-financial information, on a timely basis, in the Partnership's  reports
to  the  SEC.   Disclosure controls and procedures  include  all  processes
necessary  to  ensure  that material information  is  recorded,  processed,
summarized  and  reported within the time periods specified  in  the  SEC's
rules  and  forms,  and  is  accumulated and  communicated  to  management,
including our chief executive and chief financial officers, to allow timely
decisions regarding required disclosures.

     With respect to these disclosure controls and procedures:

          management  has  evaluated the effectiveness  of  the  disclosure
          controls  and procedures as of the end of the period  covered  by
          this report;

          this evaluation was conducted under the supervision and with  the
          participation  of management, including the chief  executive  and
          chief financial officers of the Managing General Partner; and

          it  is  the  conclusion of chief executive  and  chief  financial
          officers  of  the Managing General Partner that these  disclosure
          controls   and   procedures  are  effective  in   ensuring   that
          information  that is required to be disclosed by the  Partnership
          in   reports  filed  or  submitted  with  the  SEC  is  recorded,
          processed,  summarized  and  reported  within  the  time  periods
          specified in the rules and forms established by the SEC.

Internal Control Over Financial Reporting
There  has  not been any change in the Partnership's internal control  over
financial reporting that occurred during the quarter ended March  31,  2005
that has materially affected, or is reasonably likely to materially affect,
its internal control over financial reporting.

<PAGE>
                       PART II. - OTHER INFORMATION


Item 1.   Legal Proceedings

          None

Item 2.   Changes in Securities

          None

Item 3.   Defaults Upon Senior Securities

          None

Item 4.   Submission of Matter to a Vote of Security Holders

          None

Item 5.   Other Information

          None

Item 6.   Exhibits and Reports on Form 8-K

               (a)  Exhibits:

               31.1 Rule 13a-14(a)/15d-14(a) Certification
               31.2 Rule 13a-14(a)/15d-14(a) Certification
               32.1 Certification of Chief Executive
Officer and Chief Financial Officer
                 Pursuant to 18 U.S.C. Section 1350, as adopted
                  Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002

<PAGE>
                                SIGNATURES


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.


                                 Southwest  Royalties Institutional  Income
                          Fund
                          X-C, L.P., a Delaware limited partnership


                                        By:    Southwest  Royalties,  Inc.,
                                 Managing
                                 General Partner


                          By:    /s/ L. Paul Latham
                                 L. Paul Latham
                                 President and Chief Executive Officer



Date:  May 16, 2005

<PAGE>

                   SECTION 302 CERTIFICATION                Exhibit 31.1


I, L. Paul Latham, certify that:

1.    I  have  reviewed  this quarterly report on Form  10-Q  of  Southwest
Royalties Institutional Income Fund X-C, L.P.

2.Based  on my knowledge, this report does not contain any untrue statement
  of  a  material fact or omit to state a material fact necessary  to  make
  the  statements  made,  in light of the circumstances  under  which  such
  statements  were made, not misleading with respect to the period  covered
  by this report;

3.Based  on  my  knowledge, the financial statements, and  other  financial
  information  included  in  this report, fairly present  in  all  material
  respects  the financial condition, results of operations and  cash  flows
  of the registrant as of, and for, the periods presented in this report;

4.The  registrant's other certifying officer(s) and I are  responsible  for
  establishing  and  maintaining disclosure  controls  and  procedures  (as
  defined   in  Exchange  Act  Rules  13a-15(e)  and  15d-15(e))  for   the
  registrant and have:

  a)Designed  such  disclosure  controls and  procedures,  or  caused  such
     disclosure   controls  and  procedures  to  be  designed   under   our
     supervision,  to  ensure  that material information  relating  to  the
     registrant, including its consolidated subsidiaries, is made known  to
     us  by others within those entities, particularly during the period in
     which this report is being prepared;

  b)Evaluated  the  effectiveness of the registrant's  disclosure  controls
     and  procedures and presented in this report our conclusions about the
     effectiveness of the disclosure controls and procedures, as of the end
     of the period covered by this report based on such evaluation; and

  c)Disclosed  in  this  report  any change in  the  registrant's  internal
     control over financial reporting that occurred during the registrant's
     most recent fiscal quarter (the registrant's fourth fiscal quarter  in
     the  case  of  an annual report) that has materially affected,  or  is
     reasonably  likely  to  materially affect, the  registrant's  internal
     control over financial reporting; and

5.The  registrant's other certifying officer(s) and I have disclosed, based
  on  our  most  recent  evaluation  of  internal  control  over  financial
  reporting,  to  the  registrant's auditors and  the  audit  committee  of
  registrant's  board  of directors (or persons performing  the  equivalent
  functions):

  a)All  significant deficiencies and material weaknesses in the design  or
     operation   of   internal  control  over  financial  reporting   which
     reasonably  likely  to  adversely affect the registrant's  ability  to
     record, process, summarize and report financial information; and

  b)Any  fraud, whether or not material, that involves management or  other
     employees  who  have  a significant role in the registrant's  internal
     control over financial reporting.


Date: May 16, 2005                 /s/ L. Paul Latham
                                   L. Paul Latham
                                   President and Chief Executive Officer
                                   of Southwest Royalties, Inc., the
                                   Managing General Partner of
                                   Southwest Royalties Institutional Income
Fund X-C, L.P.




<PAGE>
                   SECTION 302 CERTIFICATION                Exhibit 31.2


I, Mel G. Riggs, certify that:

1.    I  have  reviewed  this quarterly report on Form  10-Q  of  Southwest
Royalties Institutional Income Fund X-C, L.P.

2.Based  on my knowledge, this report does not contain any untrue statement
  of  a  material fact or omit to state a material fact necessary  to  make
  the  statements  made,  in light of the circumstances  under  which  such
  statements  were made, not misleading with respect to the period  covered
  by this report;

3.Based  on  my  knowledge, the financial statements, and  other  financial
  information  included  in  this report, fairly present  in  all  material
  respects  the financial condition, results of operations and  cash  flows
  of the registrant as of, and for, the periods presented in this report;

4.The  registrant's other certifying officer(s) and I are  responsible  for
  establishing  and  maintaining disclosure  controls  and  procedures  (as
  defined   in  Exchange  Act  Rules  13a-15(e)  and  15d-15(e))  for   the
  registrant and have:

  a)Designed  such  disclosure  controls and  procedures,  or  caused  such
     disclosure   controls  and  procedures  to  be  designed   under   our
     supervision,  to  ensure  that material information  relating  to  the
     registrant, including its consolidated subsidiaries, is made known  to
     us  by others within those entities, particularly during the period in
     which this report is being prepared;

  b)Evaluated  the  effectiveness of the registrant's  disclosure  controls
     and  procedures and presented in this report our conclusions about the
     effectiveness of the disclosure controls and procedures, as of the end
     of the period covered by this report based on such evaluation; and

  c)Disclosed  in  this  report  any change in  the  registrant's  internal
     control over financial reporting that occurred during the registrant's
     most recent fiscal quarter (the registrant's fourth fiscal quarter  in
     the  case  of  an annual report) that has materially affected,  or  is
     reasonably  likely  to  materially affect, the  registrant's  internal
     control over financial reporting; and

5.The  registrant's other certifying officer(s) and I have disclosed, based
  on  our  most  recent  evaluation  of  internal  control  over  financial
  reporting,  to  the  registrant's auditors and  the  audit  committee  of
  registrant's  board  of directors (or persons performing  the  equivalent
  functions):

  a)All  significant deficiencies and material weaknesses in the design  or
     operation   of   internal  control  over  financial  reporting   which
     reasonably  likely  to  adversely affect the registrant's  ability  to
     record, process, summarize and report financial information; and

  b)Any  fraud, whether or not material, that involves management or  other
     employees  who  have  a significant role in the registrant's  internal
     control over financial reporting.


Date:  May 16, 2005                /s/ Mel G. Riggs
                                   Mel G. Riggs
                                     Vice  President  and  Chief  Financial
Officer of
                                   Southwest Royalties, Inc., the
                                   Managing General Partner of
                                   Southwest Royalties Institutional Income
Fund X-C, L.P.


<PAGE>
                                                               Exhibit 32.1

               CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND
                          CHIEF FINANCIAL OFFICER

Pursuant to 18 U.S.C.  1350 and in connection with the accompanying  report
on  Form  10-Q  for  the period ended March 31, 2005 that  is  being  filed
concurrently with the Securities and Exchange Commission on the date hereof
(the  "Report"),  each of the undersigned officers of  Southwest  Royalties
Institutional Income Fund X-C, L.P. (the "Company"), hereby certifies that:

     1.    The Report fully complies with the requirements of section 13(a)
     or 15(d) of the Securities Exchange Act of 1934; and

     2.   The  information contained in the Report fairly presents, in  all
          material  respects,  the  financial  condition  and  results   of
          operation of the Company.


                                   /s/ L. Paul Latham
                                   L. Paul Latham
                                   President and Chief Executive Officer
                                        of Southwest Royalties, Inc., the
                                        Managing General Partner of
                                         Southwest  Royalties Institutional
                                   Income Fund X-C, L.P.

                                   May 16, 2005


                                   /s/ Mel G. Riggs
                                   Mel G. Riggs
                                   Vice   President  and  Chief   Financial
                                   Officer of
                                        Southwest Royalties, Inc., the
                                        Managing General Partner of
                                         Southwest  Royalties Institutional
                                   Income Fund X-C, L.P.

                                   May 16, 2005