NEWSROOM

    TORONTO, May 20 /CNW/ - Pacific Rubiales Energy Corp. (TSX: PEG)
announced today the filing of on SEDAR (www.sedar.com) of six independent
resource assessment reports (the Resource Reports) prepared by Petrotech
Engineering Ltd. (Petrotech), of Burnaby, Canada, relating to four exploration
blocks located in Colombia and Peru respectively. Using probabilistic
analysis, Petrotech calculated a total best estimate (P50) in the four blocks
to be 258.1 million barrels of oil and 312 Bcf of gas of prospective resources
and 757.7 million barrels of oil of undiscovered resources. The Resource
Reports can also be viewed on the Company's website (www.pacificrubiales.com).
    Petrotech was retained by the Company to prepare the Resource Reports to
estimate the potential undiscovered oil and gas resources underlying the 2,940
square kilometre portion of the Arauca Technical Evaluation Agreement, in
which the Company has a 95% working interest; the 8 remaining unexplored
prospects of the 274.68 square kilometres of La Creciente Block, in which the
Company has a 100% working interest; the 1,527.36 square kilometres of the
Quifa Block, in which the Company has a 60% working interest; and the three
blocks located in the Maranon and Ucayali Basins of Peru (the Peru Blocks),
known as blocks 135, 137 and 138, with an area of 10,204, 4,489.4, 4142.2
square kilometres, respectively, in which the Company has 100% working
interest.
    Petrotech has also been retained to perform resource assessments of the
Company's interests in four other exploration properties known as the Moriche,
Tacacho, Jagueyes and Guama blocks, all located in Colombia. Petrotech and the
Company expect the resource assessments relating to such areas to be completed
within the next two months.
    The Petrotech resource estimates set out in this press release were
prepared in accordance with the requirements of Canadian National Instrument
51-101 Standards of Disclosure for Oil and Gas Activities. Capitalized terms
related to resource classifications used in this press release are based on
the definitions and guidelines in the Canadian Oil and Gas Evaluation Handbook
(COGEH).
    No commercial discoveries have been made in respect of either the Arauca
or Quifa blocks located in Colombia or the Peru Blocks, hence, there have been
no reserves found at any of these sites to date.

    Arauca Technical Evaluation Agreement (TEA)

    Undiscovered resources have been assigned to eight prospects, each
traversed with two or more separate 2-D seismic lines. Seven of the prospects
are classified as Paleozoic inverted structures at deeper levels and a
shallower prospect classified as a Tertiary antithetic faulted block. The
below table sets out the prospective oil resources for each of the eight
prospects in the Arauca Block:Gross Undiscovered        Net Undiscovered
                                       Oil Resources           Oil Resources
                                P90     P50     P10     P90     P50     P10
    Prospect Type             (MMbbl) (MMbbl) (MMbbl) (MMbbl) (MMbbl) (MMbbl)
                              -----------------------------------------------
    T-A Antithetic faulted
     block                      5.5    12.1    25.7    5.06    11.1    18.6
    Pz-A Paleozoic inverted
     structure                  4.6    29.8   170.7    4.23    27.4   157.0
    Pz-B Paleozoic inverted
     structure                  2.3    15.4    86.2    2.16    14.2    84.0
    Pz-C Paleozoic inverted
     structure                  0.8     4.9    25.6    0.73    4.58    24.0
    Pz-D Paleozoic inverted
     structure                  0.7     4.1    22.4    0.64    3.72    21.1
    Pz-E Paleozoic inverted
     structure                  0.3     2.1    12.1    0.27    1.93    11.1
    Pz-F Paleozoic inverted
     structure                  1.4    11.1    72.8    1.28    10.2    67.1
    Pz-G Paleozoic inverted
     structure                  5.0    32.0   179.0    4.60    29.4   165.0
                              -----------------------------------------------
    Total                      20.6   111.5   594.6    18.9   102.5   546.0La Creciente Block

    The below table sets out the prospective gas resources for each of the
eight prospects noted below and located in the La Creciente Block, as well as
their respective chance of success:Recoverable
    Prospects      Gas Resource     Chance of Success   Risked Gas Resource
    -------------------------------------------------------------------------
    B                160.0 Bcf              0.35              56.00 Bcf
    C                125.0 Bcf              0.45              56.25 Bcf
    E                101.0 Bcf              0.50              50.50 Bcf
    F                180.0 Bcf              0.28              50.40 Bcf
    G                101.0 Bcf              0.40              40.40 Bcf
    H                 47.5 Bcf              0.24              11.40 Bcf
    I                 83.0 Bcf              0.29              24.07 Bcf
    J                103.0 Bcf              0.22              22.66 Bcf
    -------------------------------------------------------------------------
    Total            900.5 Bcf                               311.68 BcfThe chance of success is the overall possibility of success that includes
all the geological uncertainties and risks. The estimated daily rate for the
gas resource is 108.75 MMcf of gas. Together with the 60 MMcf of gas from the
proved and probable gas reserve in the La Creciente Block, the daily rate
would be 168.75 MMcf of gas. At this rate, the estimated royalty payable would
be 8.561% for the gas and 8.0% for the condensate. As the current maximum gas
pipeline capacity is 60MMcf of gas per day, any gas found in these prospects
will be deemed non-commercial until there is a means of transportation to the
markets. Accordingly, any amount of production over the anticipated maximum
daily production rate of 60 MMcf per day will require additional pipeline and
market capacities. The Company is currently reviewing opportunities to export
any additional gas that may be produced from the block to international
markets

    Quifa Block

    The below table sets out the best estimate (P50) prospective oil
resources for the Quifa Block:Best Estimate Prospective Resources
                        100% Oil      Gross Oil        Net Oil
    Case                  (MMbbl)        (MMbbl)        (MMbbl)
    -----------------------------------------------------------
    12.5 degrees API Oil   263.5          158.1          148.8
    18.0 degrees API Oil   259.3          155.6          144.9
    -----------------------------------------------------------The gross oil is the Company's share of the working interest before
paying royalty and the net oil is the Company's share of the working interest
after deduction of the royalty. The Quifa Block is adjacent to the Company's
Rubiales field which is currently producing at a daily rate of 31,774 barrels
of heavy oil (see news release of April 19, 2008).

    Peru Blocks

    The below table sets out the low, best and high estimates (P90, P50 and
P10 respectively) for the prospective oil resources identified in the Peru
Blocks. The resources in the Peru Blocks are considered to be in the
undiscovered resource category and, therefore, are not currently considered
economically viable or recoverable. Accordingly, the cash flow values are not
required for the evaluation. The following table sets out the total
prospective resources in the three blocks.100% Oil      Gross Oil        Net Oil
    Estimate              (MMbbl)        (MMbbl)        (MMbbl)
    -----------------------------------------------------------
    P90 (low)              109.7          109.7           95.9
    P50 (best)             757.7          757.7          659.6
    P10 (high)           3,348.3        3,348.3        2,906.2
    -----------------------------------------------------------
    Mean                 1,405.2        1,405.2        1,220.6Undiscovered resources are defined as those quantities of oil and gas
estimated on a given date to be contained in accumulations yet to be
discovered. The estimated potentially recoverable portion of undiscovered
resources is classified as prospective resources. Prospective resources are
defined as those quantities of oil and gas estimated on a given date to be
potentially recoverable from undiscovered accumulations. If discovered, they
would be technically and economically viable to recover. However, there is no
certainty that the prospective resources will be discovered. In addition, the
following mutually exclusive Classification of Resources was used:

    Low Estimate - This is considered to be a conservative estimate of the
quantity that will actually be recovered from the accumulation. This term
reflects a P90 confidence level where there is a 90% chance that a successful
discovery will be more than this resource estimate.

    Best Estimate - This is considered to be the best estimate of the
quantity that will actually be recovered from the accumulation. This term is a
measure of central tendency of the uncertainty distribution and in this case
reflects a 50% confidence level where the successful discovery will have a 50%
chance of being more than this resource estimate.

    High Estimate - This is considered to be an optimistic estimate of the
quantity that will actually be recovered from the accumulation. This term
reflects a P10 confidence level where there is a 10% chance that the
successful discovery will be more than this resource estimate.

    Petrotech has acted independently in the preparation of the Report.
Petrotech and its employees have no direct or indirect ownership in the
properties appraised or the areas of study described in the reports. Mr. John
Yu, P. Eng., signed off on the reports being filed, each of which has been
prepared by him as a Qualified Reserves Evaluator, with the assistance of
others on Petrotech's staff.

    Pacific Rubiales, a Canadian-based company and producer of natural gas
and heavy crude oil, owns 100 percent of Meta Petroleum Limited, a Colombian
oil operator which operates the Rubiales and Piriri oil fields in the Llanos
Basin in association with Ecopetrol S.A. the Colombian, national oil company.
The Company is focused on identifying opportunities primarily within the
eastern Llanos Basin of Colombia as well as in other areas in Colombia and
northern Peru. Pacific Rubiales has a current net production of approximately
21,000 barrels of oil equivalent per day, with working interests in the
Rubiales, Piriri and Quifa concessions and the Caguan, Dindal, Rio Seco, Puli
B, La Creciente, Moriche, Guama, Arauca, Tacacho and Jagueyes blocks in
Colombia and blocks 135, 137 and 138 in Peru.

    All monetary amounts in U.S. dollars unless otherwise stated. This news
release contains certain "forward-looking statements" and "forward-looking
information" under applicable Canadian securities laws concerning the
business, operations and financial performance and condition of Pacific
Rubiales Energy Corp. Forward-looking statements and forward-looking
information include, but are not limited to, statements with respect to
estimated production and reserve life of the various oil and gas projects of
Pacific Rubiales; the estimation of oil and gas reserves; the realization of
oil and gas reserve estimates; the timing and amount of estimated future
production; costs of production; success of exploration activities; and
currency exchange rate fluctuations. Except for statements of historical fact
relating to the companies, certain information contained herein constitutes
forward-looking statements. Forward-looking statements are frequently
characterized by words such as "plan," "expect," "project," "intend,"
"believe," "anticipate", "estimate" and other similar words, or statements
that certain events or conditions "may" or "will" occur. Forward-looking
statements are based on the opinions and estimates of management at the date
the statements are made, and are based on a number of assumptions and subject
to a variety of risks and uncertainties and other factors that could cause
actual events or results to differ materially from those projected in the
forward-looking statements. Many of these assumptions are based on factors and
events that are not within the control of Pacific Rubiales and there is no
assurance they will prove to be correct. Factors that could cause actual
results to vary materially from results anticipated by such forward-looking
statements include changes in market conditions, risks relating to
international operations, fluctuating oil and gas prices and currency exchange
rates, changes in project parameters, the possibility of project cost overruns
or unanticipated costs and expenses, labour disputes and other risks of the
oil and gas industry, failure of plant, equipment or processes to operate as
anticipated, the business of Petro Rubiales and Pacific Stratus not being
integrated successfully or such integration proving more difficult, time
consuming or costly than expected as well as those risk factors discussed or
referred to in the annual Management's Discussion and Analysis and Annual
Information Form for Pacific Rubiales filed with the securities regulatory
authorities in all provinces of Canada and available at www.sedar.com.
Although Pacific Rubiales has attempted to identify important factors that
could cause actual actions, events or results to differ materially from those
described in forward-looking statements, there may be other factors that cause
actions, events or results not to be anticipated, estimated or intended. There
can be no assurance that forward-looking statements will prove to be accurate,
as actual results and future events could differ materially from those
anticipated in such statements. Pacific Rubiales undertakes no obligation to
update forward-looking statements if circumstances or management's estimates
or opinions should change except as required by applicable securities laws.
The reader is cautioned not to place undue reliance on forward-looking
statements. Statements concerning oil and gas reserve estimates may also be
deemed to constitute forward-looking statements to the extent they involve
estimates of the oil and gas that will be encountered if the property is
developed.
    Boe may be misleading, particularly if used in isolation. A boe
conversion ratio of 6 mcf:1 bbl is based on an energy equivalency conversion
method primarily applicable at the burner tip and does not represent a value
equivalency at the wellhead.

    %SEDAR: 00007953E