<PAGE>   1
                                                                   EXHIBIT 99(a)


              [RYDER SCOTT COMPANY PETROLEUM ENGINEERS LETTERHEAD]






                                February 3, 1997




Pennzoil Company
Post Office Box 2967
Houston, Texas  77001

Gentlemen:

                  At your request we have prepared an estimate of the reserves,
future production, and income attributable to certain leasehold and royalty
interests of Pennzoil Company including Pennzoil Exploration and Production
Company, Pennzoil Caspian Corporation, Pennzoil Resources Canada Ltd., Pennzoil
Venezuela Incorporated, Pennzoil Products Company, and Pennzoil Company
(successor to Proven Properties, Inc.) (collectively referred to herein as the
Company) as of December 31, 1996. In accordance with the requirements of FASB
69, our estimates of the Company's net proved reserves as of December 31, 1993,
1994, 1995, and 1996, as contained in this report and our previous reports, are
presented in attached Table No. 1 together with a tabulation of the components
of the differences in the estimates as of such dates. The Company's reserves in
the United States are located in all the main producing states (except Alaska),
and in state and federal waters offshore California, Louisiana, and Texas. The
Company's foreign reserves are located in Canada, Venezuela, and Azerbaijan.

                  The estimated reserve volumes and future income amounts
presented in this report are related to hydrocarbon prices. December 1996
hydrocarbon prices were used in the preparation of this report as required by
Securities and Exchange Commission (SEC) and Financial Accounting Standards
Bulletin No. 69 (FASB 69) guidelines; however, actual future prices may vary
significantly from December 1996 prices. Therefore, volumes of reserves
actually recovered and amounts of income actually received may differ
significantly from the estimated quantities presented in this report. Our
estimates of the proved net reserves attributable to the interests of the
Company as of December 31, 1996 are shown below:

<TABLE>
<CAPTION>
                                                Proved Net Reserves
                                              As of December 31, 1996
                                   --------------------------------------------
                                      Liquid, Barrels             Gas, MMCF
                                   ----------------------     -----------------
                                   
<S>                                    <C>                       <C>      
Developed and Undeveloped              
   United States                       165,124,840               1,187,240
   Foreign                              22,329,633                  89,527
                                       -----------               ---------    
      Total Worldwide                  187,454,473               1,276,767
                                       
Developed                              
   United States                       140,689,795               1,070,100
   Foreign                               1,475,810                  89,527
                                       -----------               ---------
      Total Worldwide                  142,165,605               1,159,627
</TABLE>

                  The "Liquid" reserves shown above are comprised of crude oil,
condensate, and natural gas liquids. Natural gas liquids comprise 19 percent of
the Company's developed liquid reserves and 

<PAGE>   2
Pennzoil
February 3, 1997
Page 2




15 percent of the Company's developed and undeveloped liquid reserves. All
hydrocarbon liquid reserves are expressed in standard 42 gallon barrels. All
gas volumes are hydrocarbon sales gas expressed in MMCF at the pressure and
temperature bases of the area where the gas reserves are located. Our estimates
of hydrocarbon sales gas reserves as of December 31, 1996 do not include
181,855 MMCF of carbon dioxide which is also sales gas. Revenues from carbon
dioxide sales are included in our estimates of future cash inflows as of
December 31, 1996. In addition, the Company owns 44,292 long tons of sulfur
reserves as of December 31, 1996 which are not shown above; however, the
revenue from these sulfur reserves is included in the cash inflow data in this
report. Our estimates of proved net reserves as of December 31, 1996 include
1,365,738 barrels and 4,095 MMCF for Pennzoil Venezuela, Inc. for which
Pennzoil has a contract to develop and produce but does not have actual
ownership of the hydrocarbons.

                  The proved reserves presented in this report comply with the
SEC's Regulation S-X Part 210.4-10 Sec. (a) as clarified by subsequent
Commission Staff Accounting Bulletins, and are based on the following
definitions and criteria:

              Proved reserves of crude oil, condensate, natural gas, and
       natural gas liquids are estimated quantities that geological and
       engineering data demonstrate with reasonable certainty to be recoverable
       in the future from known reservoirs under existing conditions.
       Reservoirs are considered proved if economic producibility is supported
       by actual production or formation tests. In certain instances, proved
       reserves are assigned on the basis of a combination of core analysis and
       electrical and other type logs which indicate the reservoirs are
       analogous to reservoirs in the same field which are producing or have
       demonstrated the ability to produce on a formation test. The area of a
       reservoir considered proved includes (1) that portion delineated by
       drilling and defined by fluid contacts, if any, and (2) the adjoining
       portions not yet drilled that can be reasonably judged as economically
       productive on the basis of available geological and engineering data. In
       the absence of data on fluid contacts, the lowest known structural
       occurrence of hydrocarbons controls the lower proved limit of the
       reservoir. Proved reserves are estimates of hydrocarbons to be recovered
       from a given date forward. They may be revised as hydrocarbons are
       produced and additional data become available. Proved natural gas
       reserves are comprised of non-associated, associated, and dissolved gas.
       An appropriate reduction in gas reserves has been made for the expected
       removal of natural gas liquids, for lease and plant fuel, and the
       exclusion of non-hydrocarbon gases if they occur in significant
       quantities and are removed prior to sale. Reserves that can be produced
       economically through the application of improved recovery techniques are
       included in the proved classification when these qualifications are met:
       (1) successful testing by a pilot project or the operation of an
       installed program in the reservoir provides support for the engineering
       analysis on which the project or program was based, and (2) it is
       reasonably certain the project will proceed. Improved recovery includes
       all methods for supplementing natural reservoir forces and energy, or
       otherwise increasing ultimate recovery from a reservoir, including (1)
       pressure maintenance, (2) cycling, and (3) secondary recovery in its
       original sense. Improved recovery also includes the enhanced recovery
       methods of thermal, chemical flooding, and the use of miscible and
       immiscible displacement fluids. Estimates of proved reserves do not
       include crude oil, natural gas, or natural gas liquids being held in
       underground storage. Depending on the status of development, these
       proved reserves are further subdivided into:

                  (i) "developed reserves" which are those proved reserves
              reasonably expected to be recovered through existing wells with
              existing equipment and operating methods, including (a)
              "developed producing reserves" which are those proved developed
              reserves reasonably expected to be produced from existing
              completion intervals now open for production in


<PAGE>   3
Pennzoil
February 3, 1997
Page 3




              existing wells, and (b) "developed non-producing reserves" which
              are those proved developed reserves which exist behind the
              casing of existing wells which are reasonably expected to be
              produced through these wells in the predictable future where the
              cost of making such hydrocarbons available for production should
              be relatively small compared to the cost of a new well; and

                  (ii) "undeveloped reserves" which are those proved reserves
              reasonably expected to be recovered from new wells on undrilled
              acreage, from existing wells where a relatively large expenditure
              is required, and from acreage for which an application of fluid
              injection or other improved recovery technique is contemplated
              where the technique has been proved effective by actual tests in
              the area in the same reservoir. Reserves from undrilled acreage
              are limited to those drilling units offsetting productive units
              that are reasonably certain of production when drilled. Proved
              reserves for other undrilled units are included only where it can
              be demonstrated with reasonable certainty that there is
              continuity of production from the existing productive formation.

                  Because of the direct relationship between volumes of proved
undeveloped reserves and development plans, we include in the proved
undeveloped category only reserves assigned to undeveloped locations that we
have been assured will definitely be drilled and reserves assigned to the
undeveloped portions of secondary or tertiary projects which we have been
assured will definitely be developed.

                  The Company has interests in certain tracts which have
substantial additional hydrocarbon quantities which cannot be classified as
proved and consequently are not included herein. The Company has active
exploratory and development drilling programs which may result in the
reclassification of significant additional volumes to the proved category.

                  In accordance with the requirements of FASB 69, our estimates
of future cash inflows, future costs, and future net cash inflows before income
tax as of December 31, 1996 from this report and as of December 31, 1995 from
our previous report are presented below.


<TABLE>
<CAPTION>
                                                Total Worldwide
                                             As of December 31(1)(2)
                                ------------------------------------------------
                                        1996                       1995
                                ---------------------      ---------------------
<S>                                <C>                         <C>
Future Cash Inflows                $8,958,482,749              $6,569,120,413
Future Costs                      
    Production                     $2,266,664,101              $1,954,332,406
    Development                       490,063,774                 536,689,322
                                   --------------              --------------
        Total Costs                $2,756,727,875              $2,491,021,728

Future Net Cash Inflows           
    Before Income Tax              $6,201,754,874              $4,078,098,685

Present Value at 10%              
    Before Income Tax              $3,967,371,608              $2,646,967,469
</TABLE>

------------
(1)  The cash inflow data for December 31, 1996 include revenues from 181,855
     net MMCF of carbon dioxide reserves which have a future net cash inflow
     before income tax of $56,210,214 and present value at 10 percent before
     income tax of $19,770,225. The cash inflow data for December 31, 1995
     include revenues from 156,339 net MMCF of carbon dioxide reserves which
     have a future net cash inflow before income tax of $45,992,640 and present
     value at 10 percent before income tax of $18,647,275.

(2)  The cash inflow data for December 31, 1996 includes net cash inflow before
     income tax of $14,108,210 and present value at 10 percent before income
     tax of $11,922,173 attributable to Pennzoil Venezuela, Inc. 

<PAGE>   4
Pennzoil
February 3, 1997
Page 4





                  Our estimates as of December 31, 1996 and 1995 of future cash
inflows, future costs, future net cash inflows before income tax, and present
value at 10 percent before income tax are shown individually for total
worldwide, total United States (onshore and offshore), and foreign areas in
Table No. 2 which is attached.

                  The future cash inflows are gross revenues before any
deductions. The production costs were based on current data and include
production taxes in the United States, certain foreign taxes where applicable,
ad valorem taxes, and certain other items such as transportation and processing
costs, in addition to the operating costs directly applicable to the individual
leases or wells. The development costs were based on current data and include
certain dismantlement and abandonment costs net of salvage for properties where
such costs are relatively significant.

                  The Company furnished us with gas prices in effect at
December 31, 1996 and with its forecasts of future gas prices which take into
account SEC guidelines, current market prices, contract prices, and fixed and
determinable price escalations where applicable. In accordance with SEC
guidelines, the future gas prices used in this report make no allowances for
future gas price increases which may occur as a result of inflation nor do they
account for seasonal variations in gas prices which may cause future yearly
average gas prices to be somewhat different than December gas prices. For gas
sold under contract, the contract gas price including fixed and determinable
escalations exclusive of inflation adjustments, was used until the contract
expires and then was adjusted to the current market price for the area and held
at this adjusted price to depletion of the reserves.

                  The Company furnished us with liquid prices in effect at
December 31, 1996 and these prices were held constant to depletion of the
properties. In accordance with SEC guidelines, changes in liquid prices
subsequent to December 31, 1996 were not considered in this report.

                  The Alberta Royalty Tax Credit and the British Columbia Cost
of Service Allowance were not applied in our estimates of future net income
from the Company's properties in Canada.

                  Operating costs for the leases and wells in this report were
based on the operating expense reports of the Company and include only those
costs directly applicable to the leases or wells. When applicable, the
operating costs include a portion of general and administrative costs allocated
directly to the leases and wells under terms of operating agreements.
Development costs were furnished to us by the Company and are based on
authorizations for expenditure for the proposed work or actual costs for
similar projects. The current operating and development costs were held
constant throughout the life of the properties. At the request of Pennzoil,
their estimate of zero net abandonment costs after salvage value for onshore
properties was used in this report. Ryder Scott has not performed a detailed
study of the abandonment costs nor the salvage value and makes no warranty for
Pennzoil's estimate. The estimated net cost of abandonment after salvage was
included for offshore properties where abandonment costs net of salvage are
significant. The estimates of the offshore net abandonment costs furnished by
the Company were accepted without independent verification. No deduction was
made for indirect costs such as general administration and overhead expenses,
loan repayments, interest expenses, and exploration and development
prepayments. The Company supplied data on accumulated gas production imbalances
which were taken into account in our estimates of future production and income.

                  The estimates of reserves presented herein are based upon a
detailed study of the properties in which the Company owns an interest;
however, we have not made any field examination of the properties. No
consideration was given in this report to potential environmental liabilities
which

<PAGE>   5
Pennzoil
February 3, 1997
Page 5



may exist nor were any costs included for potential liability to restore and
clean up damages, if any, caused by past operating practices. The Company has
informed us that they have furnished us all of the accounts, records,
geological and engineering data and reports, and other data required for this
investigation. The ownership interests, prices, and other factual data
furnished by the Company were accepted without independent verification. The
estimates presented in this report are based on data available through December
1996.

                  The reserves included in this report are estimates only and
should not be construed as being exact quantities. They may or may not be
actually recovered, and if recovered, the revenues therefrom and the actual
costs related thereto could be more or less than the estimated amounts.
Moreover, estimates of reserves may increase or decrease as a result of future
operations.

                  In general, we estimate that future gas production rates will
continue to be the same as the average rate for the latest available 12 months
of actual production until such time that the well or wells are incapable of
producing at this rate. The well or wells were then projected to decline at
their decreasing delivery capacity rate. Our general policy on estimates of
future gas production rates is adjusted when necessary to reflect actual gas
market conditions in specific cases. The future production rates from wells now
on production may be more or less than estimated because of changes in market
demand or allowables set by regulatory bodies. Wells or locations which are not
currently producing may start producing earlier or later than anticipated in
our estimates of their future production rates.

                  While it may reasonably be anticipated that the future prices
received for the sale of production and the operating costs and other costs
relating to such production may also increase or decrease from existing levels,
such changes were, in accordance with rules adopted by the SEC, omitted from
consideration in making this evaluation.

                  Neither we nor any of our employees have any interest in the
subject properties and neither the employment to make this study nor the
compensation is contingent on our estimates of reserves and future cash inflows
for the subject properties.

                                           Very truly yours,

                                           RYDER SCOTT COMPANY
                                           PETROLEUM ENGINEERS

                                           /S/ RAYMOND V. CRUCE

                                           Raymond V. Cruce, P.E.
                                           Chairman and CEO
RVC/sw


<PAGE>   6



                                  TABLE NO. 1

                                PENNZOIL COMPANY
                            PROVED NET RESERVE DATA(1)

<TABLE>
<CAPTION>                                                                                                                          
                                                                                                           United States            
                                                                     Total Worldwide                 Total Onshore and Offshore     
                                                         ------------------------------------     --------------------------------- 
                                                            1996         1995        1994           1996         1995        1994   
                                                         -----------  -----------  ----------     ---------    ---------   -------- 
<S>                                                          <C>           <C>         <C>           <C>          <C>        <C>   
Net Proved Liquid(3)Reserves,Millions of Barrels                                                                                   
-----------------------------------------------------                                                                              
Developed and Undeveloped                                                                                                          
   Beginning of Year                                         191.6         206.2       200.9         174.9        204.5      198.9 
      12/31/95 Est. Prepared by Outrim Szabo Assoc.                                                                                
        Ltd.(4)                                                9.6             0           0             0            0          0 
      Revisions                                               12.2         -14.9         7.9           8.1        -14.4        7.9 
      Extensions and Discoveries                              23.2          20.4        18.0          10.5         18.9       17.9 
      Improved Recovery                                        2.1           2.7         0.6           2.1          2.7        0.6 
      Estimated Production                                   -21.6         -22.1       -24.6         -20.4        -21.9      -24.3 
      Purchase of Reserves In-Place                            8.1          22.2         7.6           7.0          8.0        7.6 
      Sales of Reserves In-Place                             -37.8         -22.9        -4.2         -17.1        -22.9       -4.1 
                                                         ----------   -----------  ----------     ---------    ---------  -------- 
End of Year                                                  187.4         191.6       206.2         165.1        174.9      204.5 
                                                                                                                                   
Developed                                                                                                                          
   Beginning of Year(5)                                      152.6         177.7       164.2         151.2        176.1      162.3 
   End of Year                                               142.2         152.6       177.7         140.7        151.2      176.1 
                                                                                                                          
Net Proved Gas(6) Reserves,                                                                                               
Billions of Cubic Feet                                                                                                    
-----------------------------------------------------                                                                     
Developed and Undeveloped                                                                                                 
   Beginning of Year                                         1,291         1,376       1,491         1,256        1,341      1,453
      12/31/95 Est.  Prepared by Outrim Szabo Assoc.                                                                              
        Ltd.(4)                                                178             0           0             0            0          0
                                                                                                                                  
      Revisions                                                 61            51          12            38           56         15
      Extensions and Discoveries                               172           219         203           143          211        200
      Improved Recovery                                          2             1         Neg             2            1        Neg
      Estimated Production                                    -219          -220        -247          -202         -218       -244
      Purchase of Reserves In-Place                             36            26          14             8           26         14
      Sales of Reserves In-Place                              -244          -162         -97           -58         -161        -97
                                                         ----------   -----------  ----------     ---------    ---------  --------
End of Year                                                  1,277         1,291       1,376         1,187        1,256      1,341
                                                                                                                                  
Developed                                                                                                                         
   Beginning of Year(5)                                      1,161         1,273       1,341         1,132        1,242      1,306
   End of Year                                               1,160         1,161       1,273         1,070        1,132      1,242
<CAPTION>
                                                         
                                                                     Foreign(2)
                                                         ----------------------------------
                                                          1996          1995         1994
                                                         --------      --------     -------
<S>                                                         <C>            <C>         <C>
Net Proved Liquid(3)Reserves,Millions of Barrels         
-----------------------------------------------------    
Developed and Undeveloped                                
   Beginning of Year                                        16.7           1.7         2.0
      12/31/95 Est. Prepared by Outrim Szabo Assoc.      
        Ltd.(4)                                              9.6             0           0
      Revisions                                              4.1          -0.5         Neg
      Extensions and Discoveries                            12.7           1.5         0.1
      Improved Recovery                                        0             0           0
      Estimated Production                                  -1.2          -0.2        -0.3
      Purchase of Reserves In-Place                          1.1          14.2           0
      Sales of Reserves In-Place                           -20.7           Neg        -0.1
                                                         --------      --------     -------
End of Year                                                 22.3          16.7         1.7
                                                         
Developed                                                
   Beginning of Year(5)                                      1.3           1.6         1.9
   End of Year                                               1.5           1.3         1.6
                                                         
Net Proved Gas(6) Reserves,                              
Billions of Cubic Feet                                   
-----------------------------------------------------    
Developed and Undeveloped                                
   Beginning of Year                                          35            35          38
      12/31/95 Est.  Prepared by Outrim Szabo Assoc.     
        Ltd.(4)                                              178             0           0
                                                         
      Revisions                                               23            -5          -3
      Extensions and Discoveries                              29             8           3
      Improved Recovery                                        0             0           0
      Estimated Production                                   -17            -2          -3
      Purchase of Reserves In-Place                           28             0           0
      Sales of Reserves In-Place                            -186            -1         Neg
                                                         --------      --------     -------
End of Year                                                   90            35          35
                                                         
Developed                                                
   Beginning of Year(5)                                       29            31          35
   End of Year                                                90            29          31
</TABLE>


-----------
(1)  All reserve changes in 1994 and 1995 were categorized by Ryder Scott
     Company. Reserve changes due to extensions and discoveries and improved
     recovery during 1996 were categorized by Ryder Scott Company. The
     remaining reserve changes during 1996 were categorized by the Company.
(2)  1995 includes 1.2 million barrels and 5 billion cubic feet and 1996
     includes 1.4 million barrels and 4 billion cubic feet of natural gas in
     Venezuela for which Pennzoil has a contract to develop and produce but
     does not have actual ownership of the hydrocarbons.
(3)  Liquid reserves shown above are comprised of crude oil, condensate, and
     natural gas liquids.
(4)  These estimates were prepared by Outrim Szabo Associates, Ltd. for
     Pennzoil Petroleums, Ltd. as of December 31, 1995. The reserves
     attributable to Pennzoil Petroleums, Ltd. were sold during 1996. These
     estimates are included at the Company's request in order to reconcile
     reserve revisions. Ryder Scott Company has not reviewed these reserve
     estimates and therefore expresses no opinion as to their validity.
(5)  Beginning of year proved developed gas and liquid reserves for 1996
     excludes proved developed reserves estimated by Outrim Szabo Assoc. Ltd.
     for Pennzoil Petroleums, Ltd. as of December 31, 1995.
(6)  Excludes carbon dioxide reserve and production data. 



<PAGE>   7




                                  TABLE NO. 2

                                PENNZOIL COMPANY
                           CASH INFLOW AND COST DATA(1)
                           (MILLIONS OF U.S. DOLLARS)





<TABLE>
<CAPTION>
                                                               United States
                                   Total Worldwide          Onshore and Offshore          Foreign
                                  As of December 31           As of December 31      As of December 31
                            --------------------------    ------------------------  -------------------
                               1996            1995          1996          1995        1996       1995 
                            -----------     ----------    ---------     ----------  ---------   -------
                                                                                                       
<S>                           <C>             <C>           <C>           <C>           <C>        <C> 
Future Cash Inflows(2)        $8,958          $6,569        $8,270        $6,287        $688       $282
                                                                                                       
Future Costs                                                                                           
   Production(3)             -$2,267         -$1,954       -$2,055       -$1,849       -$212      -$105
   Development(4)               -490            -537          -445          -480         -45        -57
                              ------          ------        ------        ------        ----       ----
                                                                                                       
Total Costs                  -$2,757         -$2,491       -$2,500       -$2,329       -$257      -$162
                                                                                                       
Future Cash Inflows                                                                                    
   Before Income Tax          $6,201          $4,078        $5,770        $3,958        $431       $120
                                                                                                       
Present Value @ 10%                                                                                    
   Before Income Tax          $3,967          $2,647        $3,697        $2,587        $270      $  60
                                                                        
</TABLE>


-------- 

(1)  Data for 1996 and 1995 include cash inflows and costs attributable to
     carbon dioxide reserves located in the United States. The 1996 carbon
     dioxide reserves account for $56.2 million of cash inflows before income
     tax and $19.8 million of present value at 10% before income tax. The 1995
     carbon dioxide reserves account for $46.0 million of future cash inflows
     before income tax and $18.6 million of present value at 10% before income
     tax.
(2)  Gross revenues are before any deductions.
(3)  Includes production taxes in the U.S.A., certain foreign taxes where
     applicable, ad valorem taxes, and certain other items such as
     transportation and processing charges.
(4)  Includes future dismantlement and abandonment costs net of salvage for
     offshore properties where such costs are relatively significant.