March 14, 2006

Mr. Benjamin W. Hulburt
Rex Energy
1965 Waddle Road
State College, Pennsylvania 16803

Dear Mr. Hulburt:

In accordance with your request, we have estimated the proved reserves and
future revenue, as of December 31, 2005, to the interest of Douglas Oil & Gas
LP; Douglas Westmoreland LP; Midland Exploration LP; Penntex Resources Illinois,
Inc.; Penntex Resources LP; and Rex Energy Royalties LP (collectively referred
to herein as "Rex Energy et al.") in certain oil and gas properties located in
the United States, as listed in the accompanying tabulations. This is a revision
of our report dated March 8, 2006. The estimates in this report have been
revised to reflect the removal of contract wells in Westmoreland County,
Pennsylvania. This report has been prepared using constant prices and costs, as
discussed in subsequent paragraphs of this letter. The estimates of reserves and
future revenue in this report conform to the guidelines of the Securities and
Exchange Commission (SEC).

As presented in the accompanying summary projections, Tables I through IV, we
estimate the net reserves and future net revenue to the Rex Energy et al.
interest in these properties, as of December 31, 2005, to be:

<TABLE>
<CAPTION>
                                        Net Reserves                       Future Net Revenue ($)
                               ------------------------------         --------------------------------
                                  Oil                 Gas                                Present Worth
     Category                  (Barrels)             (MCF)               Total              at 10%
                               ---------           ----------         -----------         -----------
<S>                            <C>                  <C>               <C>                  <C>
Proved Developed
  Producing                    4,000,256            7,898,777         161,661,800          90,232,800
  Non-Producing                  337,001              301,192          16,007,300           7,089,000
Proved Undeveloped               488,754            2,926,867          30,478,800          11,563,600
                               ---------           ----------         -----------         -----------
    Total Proved               4,826,011           11,126,836         208,147,900         108,885,400
</TABLE>

The oil reserves shown include crude oil and condensate. Oil volumes are
expressed in barrels that are equivalent to 42 United States gallons. Gas
volumes are expressed in thousands of cubic feet (MCF) at standard temperature
and pressure bases.

The estimates shown in this report are for proved developed producing, proved
developed non-producing, and proved undeveloped reserves. In accordance with SEC
guidelines, our estimates do not include any probable or possible reserves that
may exist for these properties. This report does not include any value that
could be attributed to interests in undeveloped acreage beyond those tracts for
which undeveloped reserves have been estimated. Definitions of all reserve
categories are presented immediately following this letter. As shown in the
Table of Contents, for each reserve category this report includes a summary
projection of reserves and revenue along with one-line summaries of reserves,
economics, and basic data by lease.

Future gross revenue to the Rex Energy et al. interest is prior to deducting
state production taxes and ad valorem taxes. Future net revenue is after
deductions for these taxes, future capital costs, and operating expenses but

<PAGE>

before consideration of federal income taxes. In accordance with SEC guidelines,
the future net revenue has been discounted at an annual rate of 10 percent to
determine its "present worth." The present worth is shown to indicate the effect
of time on the value of money and should not be construed as being the fair
market value of the properties.

For the purposes of this report, we did not perform any field inspection of the
properties, nor did we examine the mechanical operation or condition of the
wells and their related facilities. We have not investigated possible
environmental liability related to the properties; therefore, our estimates do
not include any costs due to such possible liability. Also, our estimates do not
include any salvage value for the lease and well equipment or the cost of
abandoning the properties.

Oil prices used in this report either are the fixed contract price or are based
on a December 31, 2005, West Texas Intermediate posted price of $57.75 per
barrel and are adjusted by lease for quality, transportation fees, and regional
price differentials. In accordance with the SEC guidelines, the fixed contract
prices for properties located in Illinois and Indiana are held constant until
contract expiration. At contract expiration, the prices are adjusted to the
December 31, 2005, posted price and held constant thereafter. All other oil
prices are held constant in accordance with SEC guidelines.

Gas prices used in this report are based on a December 31, 2005, Henry Hub spot
market price of $10.08 per MMBTU and are adjusted by lease for energy content
and regional price differentials. Gas prices are held constant in accordance
with SEC guidelines.

Lease and well operating costs used in this report are based on operating
expense records of Rex Energy et al. For nonoperated properties, these costs
include the per-well overhead expenses allowed under joint operating agreements
along with estimates of costs to be incurred at and below the district and field
levels. As requested, lease and well operating costs for the operated properties
include only direct lease- and field-level costs. For all properties,
headquarters and general and administrative overhead expenses of Rex Energy et
al. are not included. Lease and well operating costs are held constant in
accordance with SEC guidelines. Capital costs are included as required for
workovers, new development wells, and production equipment.

We have made no investigation of potential gas volume and value imbalances
resulting from overdelivery or underdelivery to the Rex Energy et al. interest.
Therefore, our estimates of reserves and future revenue do not include
adjustments for the settlement of any such imbalances; our projections are based
on Rex Energy et al. receiving its net revenue interest share of estimated
future gross gas production.

The reserves shown in this report are estimates only and should not be construed
as exact quantities. The reserves may or may not be recovered; if they are
recovered, the revenues therefrom and the costs related thereto could be more or
less than the estimated amounts. Because of governmental policies and
uncertainties of supply and demand, the sales rates, prices received for the
reserves, and costs incurred in recovering such reserves may vary from
assumptions made while preparing this report. Also, estimates of reserves may
increase or decrease as a result of future operations.

In evaluating the information at our disposal concerning this report, we have
excluded from our consideration all matters as to which the controlling
interpretation may be legal or accounting, rather than engineering and geologic.
As in all aspects of oil and gas evaluation, there are uncertainties inherent in
the interpretation of engineering and geologic data; therefore, our conclusions
necessarily represent only informed professional judgment.

The titles to the properties have not been examined by Netherland, Sewell &
Associates, Inc., nor has the actual degree or type of interest owned been
independently confirmed. The data used in our estimates were obtained from Rex

<PAGE>

Energy, public data sources, and the nonconfidential files of Netherland, Sewell
& Associates, Inc. and were accepted as accurate. Supporting geologic, field
performance, and work data are on file in our office. We are independent
petroleum engineers, geologists, geophysicists, and petrophysicists; we do not
own an interest in these properties and are not employed on a contingent basis.

                                        Very truly yours,

                                        NETHERLAND, SEWELL & ASSOCIATES, INC.


                                        By: /s/ Frederic D. Sewell, P.E.
                                            Frederic D. Sewell, P.E.
                                            Chairman and Chief Executive Officer


                                        By: /s/ Matthew T. Brogdon, P.E.
                                            Matthew T. Brogdon, P.E.
                                            Petroleum Engineer

                                        Date Signed: March 14, 2006

MTB:EKK

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