1

                                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 June 30, 2006

                                    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 033-47668-03

         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 large accelerated  filer,
an  accelerated  filer,  or  a non-accelerated  filer.  See  definition  of
"accelerated  filer  and large accelerated filer"  in  Rule  12b-2  of  the
Exchange Act. (Check one):
      Large accelerated filer ___        Accelerated filer ___         Non-
accelerated filer  X

Indicate  by  check  mark whether the registrant is  a  shell  company  (as
defined in Rule 12b-2 of the Exchange Act).
                                                            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 20.

<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.

     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  natural
gas  reserves  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>

     Standardized  measure  of discounted future net  cash  flows.  Present
value  of  proved reserves, as adjusted to give effect to estimated  future
abandonment costs, net of the estimated salvage value of related equipment.

     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, 2005, which are found in the Registrant's Form
10-K  Report  for  2005 filed with the Securities and Exchange  Commission.
The December 31, 2005 balance sheet included herein has been taken from the
Registrant's  2005 Form 10-K Report.  Operating results for the  three  and
six month periods ended June 30, 2006 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

                                 June 30,  December
                                             31,
                                   2006      2005
                                   ----      ----
                                 (unaudit
                                   ed)
Assets
----------
Current assets:
 Cash and cash equivalents    $  8,493     51,969
  Receivable  from  Managing     66,722    83,656
General Partner
 Other                           1,212     1,166
                                 --------  --------
                                 ----      ----
   Total current assets          76,427    136,791
                                 --------  --------
                                 ----      ----
Oil  and  gas  properties  -
using the full-
 method of accounting            2,267,58  2,267,58
                                 7         7
       Less      accumulated
depreciation,
         depletion       and     2,243,32  2,243,32
amortization                     1         1
                                 --------  --------
                                 ----      ----
      Net   oil   and    gas     24,266    24,266
properties
                                 --------  --------
                                 ----      ----
                              $  100,693   161,057
                                 =======   =======
Liabilities  and   Partners'
Equity
----------------------------
-----------

Asset retirement obligation   $  584,520   705,381
                                 --------  --------
                                 ----      ----

Partners' (deficit):
 General partners                (89,264)  (95,079)
 Limited partners                (394,563  (449,245
                                 )         )
                                 --------  --------
                                 ----      ----
   Total partners' (deficit)     (483,827  (544,324
                                 )         )
                                 --------  --------
                                 ----      ----
                              $  100,693   161,057
                                 =======   =======













                  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   Six Months Ended
                                        June 30,            June 30,
                                     2006      2005      2006      2005
                                    -----     -----     -----     -----
Revenues
-------------
Income    from   net   profits  $  166,540   102,916   261,732   221,178
interests
Interest                           384       137       864       272
Gain  on sale of property  and     -         -         144,900   -
equipment
                                   --------  --------  --------  --------
                                   --        --        --        --
                                   166,924   103,053   407,496   221,450
                                   --------  --------  --------  --------
                                   --        --        --        --
Expenses
-------------
Depreciation,  depletion   and     -         1,477     -         3,137
amortization
Accretion expense                  12,157    9,907     24,039    19,813
General and administrative         18,229    13,287    31,846    26,263
                                   --------  --------  --------  --------
                                   --        --        --        --
                                   30,386    24,671    55,885    49,213
                                   --------  --------  --------  --------
                                   --        --        --        --
Net income                      $  136,538   78,382    351,611   172,237
                                   ======    ======    ======    ======
Net income allocated to:
 Managing General Partner       $  12,289    7,187     31,645    15,783
                                   ======    ======    ======    ======
 General Partner                $  1,365     799       3,516     1,754
                                   ======    ======    ======    ======
 Limited Partners               $  122,884   70,396    316,450   154,700
                                   ======    ======    ======    ======
  Per limited partner unit      $    20.54     11.77     52.89     25.86
                                   ======    ======    ======    ======




















                  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)

                                       Six Months Ended
                                           June 30,
                                        2006      2005
                                       -----     -----
Cash    flows   from    operating
activities:

  Cash received from income  from  $  278,620   217,954
net profits interests
 Cash paid to suppliers               (31,846)  (26,263)
 Interest received                    864       272
                                      --------  --------
                                      --        --
   Net cash provided by operating     247,638   191,963
activities
                                      --------  --------
                                      --        --
Cash    flows   from    financing
activities:

 Distributions to partners            (291,114  (200,000
                                      )         )
 Increase in distribution payable     -         196
                                      --------  --------
                                      --        --
   Net  cash  used  in  financing     (291,114  (199,804
activities                            )         )
                                      --------  --------
                                      --        --

Net  decrease  in cash  and  cash     (43,476)  (7,841)
equivalents

 Beginning of period                  51,969    32,864
                                      --------  --------
                                      --        --
 End of period                     $  8,493     25,023
                                      ======    ======
Reconciliation of net  income  to
net
   cash   provided  by  operating
activities:

Net income                         $  351,611   172,237

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

   Depreciation,  depletion   and     -         3,137
amortization
  Gain  on  sale of property  and     (144,900  -
equipment due to farmout              )
  Accretion  of asset  retirement     24,039    19,813
obligation
     Decrease    (increase)    in     16,888    (3,224)
receivables
                                      --------  --------
                                      --        --
Net  cash  provided by  operating  $  247,638   191,963
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  capital  100%      -
contributions
Oil and gas sales             90%       10%
All other revenues            90%       10%
Organization  and   offering  100%      -
costs (1)
Syndication costs             100%      -
Amortization of organization  100%      -
costs
Property acquisition costs    100%      -
Gain/loss    on     property  90%       10%
disposition
Operating and administrative  90%       10%
costs (2)
Depreciation, depletion  and
amortization
 of oil and gas properties    100%      -
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 June 30, 2006, and  for  the
     three  and  six  months  ended June 30, 2006, 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, 2005.

     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.   Asset Retirement Obligations

     Changes  in abandonment obligations for the six months ended June  30,
     2006 and 2005 are as follows:

                                        2006     2005
                                       -------  -------
Beginning of period                 $  705,381  798,702
Accretion expense                      24,039   19,814
Reduction due to farm-out              (144,90  -
                                       0)
                                       -------  -------
                                       -------  -----
End of period                       $  584,520  818,516
                                       =======  =======
                                       =



<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, and the offering of limited partnership interests
concluded 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 fluctuate 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 June 30, 2006, 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
June  30,  2006,  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>
Supplemental Information
The following unaudited information is intended to supplement the financial
statements  included  in  this Form 10-Q with  data  that  is  not  readily
available from those statements.

                             Three Months Ended
                                  June 30,
                               2006      2005
                              ------    ------
Oil production in            4,940     5,071
barrels
Gas production in mcf        3,570     2,483
Total (BOE)                  5,535     5,485
Average price per barrel  $    64.17
of oil                                 49.43
Average price per mcf of  $     5.95
gas                                    6.98
Partnership               $  151,114   100,000
distributions
Limited partner           $  135,768   90,000
distributions
Per unit distribution to  $    22.69
limited partners                       15.04
Number of limited            5,983     5,983
partner units

Operating Results
The  following discussion compares our results for the quarters ended  June
30, 2006 and 2005.  Unless otherwise indicated, references to 2006 and 2005
within this section refer to the respective quarterly period.

Income from net profits
Oil  and  gas  prices continued to climb to record levels compared  to  the
previous  two  years.  Comparing 2006 to 2005, oil and gas sales  increased
$70,200,  of  which  price variances accounted for a $69,100  increase  and
production variances accounted for a $1,100 increase.

Production  in  2006  (on a BOE basis) was 1% higher than  2005.   Our  oil
production  decreased  3%  in  2006  due  primarily  to  normal  production
declines.   Our  gas  production  was 44% higher  in  2006  than  2005  due
primarily to improved performance on one property.

In  2006,  our  realized  oil price was 30% higher  than  2005,  while  our
realized  gas price was 15% lower.  Historically, the markets for  oil  and
gas have been volatile, and they are likely to continue to be volatile.  We
have  very little control over the prices we receive for our production  at
the  wellhead since most of our physical marketing arrangements are market-
sensitive.

Oil  and gas production costs on a BOE basis increased from $30.10 per  BOE
in  2005 to $31.02 per BOE in 2006.  The increase in oil and gas production
costs  in 2006 was due primarily to higher production tax costs related  to
higher product prices.

Expenses
Depletion  on  a  BOE  basis decreased 100% in 2006.  The  properties  have
previously  been  depleted  below  estimated  salvage  value,  consequently
depletion has not been recorded in the current period

Accretion  expense  increased 23% in 2006 due primarily to  fourth  quarter
2005  revisions in previous estimates related to increased  costs  to  plug
wells..

General  and administrative ("G&A") expenses were 37% higher than  2006  as
compared  to 2005.  The increase in general and administrative expenses  is
primarily due to higher professional fees for audit and tax services.


<PAGE>
Supplemental Information
The following unaudited information is intended to supplement the financial
statements  included  in  this Form 10-Q with  data  that  is  not  readily
available from those statements.

                              Six Months Ended
                                  June 30,
                               2006      2005
                              ------    ------
Oil production in            9,341     10,741
barrels
Gas production in mcf        5,738     4,844
Total (BOE)                  10,297    11,548
Average price per barrel  $    60.94
of oil                                 48.53
Average price per mcf of  $     5.96
gas                                    5.53
Partnership               $  291,114   200,000
distributions
Limited partner           $  261,768   180,000
distributions
Per unit distribution to  $    43.75
limited partners                       30.09
Number of limited            5,983     5,983
partner units

Operating Results
The following discussion compares our results for the six months ended June
30, 2006 and 2005.  Unless otherwise indicated, references to 2006 and 2005
within this section refer to the respective six months period.

Income from net profits
Oil  and  gas  prices continued to climb to record levels compared  to  the
previous  two  years.  Comparing 2006 to 2005, oil and gas sales  increased
$55,400,  of  which price variances accounted for a $118,400  increase  and
production variances accounted for a $63,000 decrease.

Production  in  2006  (on a BOE basis) was 11% lower than  2005.   Our  oil
production decreased 13% in 2006 due primarily to reduced oil sales  volume
on  a  property  resulting from working interest  earned  by  the  Managing
General  Partner under a farm-out arrangement.  Our gas production was  18%
higher  in  2006  than 2005 due primarily to improved  performance  on  one
property.

In  2006,  our  realized  oil price was 26% higher  than  2005,  while  our
realized  gas price was 8% higher.  Historically, the markets for  oil  and
gas have been volatile, and they are likely to continue to be volatile.  We
have  very little control over the prices we receive for our production  at
the  wellhead since most of our physical marketing arrangements are market-
sensitive.

Oil  and gas production costs on a BOE basis increased from $28.30 per  BOE
in  2005 to $33.19 per BOE in 2006.  The increase in oil and gas production
costs  in  2006  was due primarily to well services on a  well  and  higher
production taxes related to higher product prices.

Gain on Sale of Property and Equipment
A  waterflood pilot project was initiated on the Section 143  Unit  in  the
first  quarter of 2006. The partnership's development cost in this  project
will  be paid by the Managing General Partner under the terms of a farm-out
arrangement  where the MGP will earn 85% of the partnership's  interest  in
the  unit and the partnership will retain a 15% interest. The reduction  in
working  interest resulted in a decrease of the asset retirement obligation
of  $144,900  that  was  recorded as a gain on the  sale  of  property  and
equipment.

Expenses
Depletion  on  a  BOE  basis decreased 100% in 2006.  The  properties  have
previously  been  depleted  below  estimated  salvage  value,  consequently
depletion has not been recorded in the current period.

Accretion  expense  increased 21% in 2006 due primarily to  fourth  quarter
2005  revisions in previous estimates related to increased  costs  to  plug
wells.

General  and administrative ("G&A") expenses were 21% higher than  2006  as
compared  to 2005.  The increase in general and administrative expenses  is
primarily due to higher professional fees for audit and tax services.

Liquidity and Capital Resources
Partnership  distributions during the quarter ending  June  30,  2006  were
$291,114,  of  which $261,768 was distributed to the limited  partners  and
$29,346  to  the  general  partners.   Cumulative  cash  distributions   of
$4,440,175  have been made to the general and limited partners as  of  June
30,  2006.  As of June 30, 2006, $4,013,410 or $670.80 per limited  partner
unit  has  been distributed to the limited partners, representing  134%  of
contributed capital.

<PAGE>
Texas Margin Taxes

In  May  2006, the State of Texas adopted House Bill 3, which modified  the
state's  franchise  tax  structure, replacing the  previous  tax  based  on
capital  or  earned  surplus with a margin tax  (the  "Texas  Margin  Tax")
effective with franchise tax reports filed on or after January 1, 2008. The
Texas  margin Tax is computed by applying the applicable tax rate  (1%  for
the  Partnership's  business)  to the profit  margin,  which  is  generally
determined  by total revenue less either cost of goods sold or compensation
as   applicable.   However  the  Partnership  believes,   based   on   it's
interpretation, that the Texas Margin Tax does not apply to the Partnership
since  substantially  all  of it's income is derived  from  a  net  profits
interest.

Recent Accounting Pronouncements

There  were  no  recent accounting pronouncements that  had  a  significant
effect on the partnership.




<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 six months ended June 30, 2006
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:  August 11, 2006



<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: August 11, 2006              /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:  August 11, 2006             /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 June 30, 2006  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.

                                   August 11, 2006


                                   /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.

                                   August 11, 2006