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IPAA - OGIS April, 2004 Gerald Schlief Sr. Vice
President Al Reese, Jr. Sr. Vice President and
CFO
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Cautionary Statement Regarding Forward-looking
Statements

• This presentation includes forward-looking
  statements and projections, made in reliance on
  the safe harbor provisions of the Private
  Securities Litigation Reform Act of 1995. The
  Company has made every reasonable effort to
  ensure that the information and assumptions on
  which these statements and projections are based
  are current, reasonable, and complete. However,
  a variety of factors could cause actual results
  to differ materially from the projections,
  anticipated results or other expectations
  expressed in this presentation, including,
  without limitation, changes in commodity prices
  for oil and natural gas estimates of reserves
  future production and operating costs marketing
  and commodity price risk management activities.
  While the Company makes these statements and
  projections in good faith, neither the Company
  nor its management can guarantee that anticipated
  future results will be achieved. The Company
  assumes no obligation to publicly update or
  revise any forward-looking statements made herein
  or any other forward-looking statements made by
  the Company, whether as a result of new
  information, future events, or otherwise.

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Company Overview

• Founded in 1991 as a development and production
  company
• Low-risk (development only), geographically
  focused operations
• 100 offshore - Gulf of Mexico (67) and North
  Sea (33)
• Strong proved reserve base at December 31, 2003
• Proved reserves of 303 Bcfe
• SEC PV-10 of 776 million (547 million after
  tax)
• Reserves are prepared by independent reservoir
  engineering firms
• 10 year production profile based on current
  development program
• 99 of reserves operated by ATP
• Substantial proved undeveloped drilling inventory
• Highly successful development track record
• Brought 35 of 36 proved undeveloped (PUD)
  projects to commercial production
• 97 success rate

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Areas of Operations

• 50 blocks in the Gulf of Mexico
• 12 blocks in the North Sea

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Business Strategy

• Acquisition and development of proved reserves
  with the following characteristics
• Primarily proved undeveloped reserves
• Close proximity to developed markets
• Existing infrastructure of pipelines and
  platforms
• Stable regulatory environment
• High working interests and operating control
• Develop projects to key value creation point
• No exploration risks

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History
Phase I InitialOperations
Phase II Expansion
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• Year-End
• Oil and Gas
• Reserves

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Types of Reserve Report

• The level of involvement by the independent
  engineering firm can vary dramatically and
  generally falls within three categories Review,
  Audit or Prepared.
• Review The independent engineering firm
  analyzes the processes and procedures that the
  company uses in estimating reserves to assure
  they comply with relevant standards. Least
  reliable independent method.
• Audit Generally means that, within a level of
  tolerance, a detailed examination of the
  companys reserves by the independent engineering
  firm has come within the companys estimate. The
  independent engineering firm focuses on
  properties that account for 70-90 of the
  companys PV-10. If the companys estimate
  falls within the independent engineering firms
  level of tolerance, then the companys estimate
  will be presented as fact. The level of
  tolerance is typically 10.
• Prepared A detailed and thorough evaluation of
  the companys reserves. The independent
  engineering firm performs a comprehensive
  examination and evaluation of all available
  source data and prepares the reserve report based
  upon its estimates. The reserve report
  represents estimates of the independent
  engineering firm, not those of the company. Most
  reliable independent method and the method used
  by ATP from inception.

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History of Increasing Reserves
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Proved Reserves Summary

• As of 12/31/2003
• 32 increase over 2002
• 2003 reserve replacement ratio 526

Since December 31, 2003, ATP has moved more than
20 Bcfe with a SEC PV-10 value of more than 80
million from Proved Undeveloped to Proved
Developed.
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Location and Composition of Reserves

• Proved Reserves By Region

Proved Reserves By Commodity
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• Prior, Current, and Future Developments

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Brazos 544

• Key Features
• Acquired 1996
• 96 developed
• Cumulative production of proved, probable and
  possible reserves has exceeded original third
  party estimates by more than 160
• 100 working interest
• Development Plans
• Gross production 10.0 MMcf/d
• Compression installed February 2004 current
  gross production 15 MMcf/d
• Behind pipe zones still to be produced

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Garden Banks 409 (Ladybug)

• Key Features
• Acquired in 2000
• Initial 2001 production rate 8,000 Bbl/d, current
  2004 rate gt 3,000 Bbl/d
• Cumulative gross production gt 5.5 million Boe and
  150 million in revenues
• Still producing from initial zones
• ATP operates with 50 working interest
• Unocal is partner
• Companys first deepwater (1,360)
  subsea development project
• Two subsea wells tied back to GB 189
• Longest oil subsea tieback (17.4 miles) in the
  world when installed

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Helvellyn

• Key Features
• Acquired in 2001
• Began production February 2004
• Current production of 60 MMcfe/d gross and 30
  MMcfe/d net
• ATP operates with a 50 working interest
• Water depth less than 120 feet (40 meters)

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Multi-Year Development Inventory

• Quality inventory of 247 Bcfe of proved
  undeveloped reserves (19 properties)
• 3 years of development opportunities without any
  future acquisitions
• 8 Gulf of Mexico properties included in 2004
  development (3 already on production)
• Emerald Field (North Sea), potentially ATPs
  largest property, not yet included in ATPs
  proved reserves

ATP operates 100 of its future developments.
97 Success rate in converting PUDs to PD
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2004 Scheduled Development Program

• Gulf of Mexico
• Garden Banks 186 (On production March 2004)
• Ship Shoal 358 (1st well on production March
  2004, 2nd well completing, 3rd well to be
  drilled)
• Matagorda Island 709 (On production March 2004)
• Eugene Island 30/71
• West Cameron 237 (Two well re-entry and side
  track beginning April/May 2004)
• West Cameron 101
• East Cameron 240
• West Cameron 432
• North Sea
• Helvellyn (On production February 2004)
• Venture (UK)
• Emerald (UK) (Shoot proprietary 3-D seismic
  Summer 2004)
• Block L-06d (Netherlands)
• Existing infrastructure in place
• Note The above developments are those
  scheduled as of April 2004. Actual developments
  will be reported during the year, which may vary
  from those listed above.

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Second Quarter Developments
GOM

• Major 2Q04 developments in progress
• SS 358 2 3
• MI 709
• WC 237 1 2

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Second Quarter Development Activities

• Ship Shoal 358 water depth 385
• At Ship Shoal 358, the first well was placed on
  production March 21, 2004. The Ship Shoal 358
  A-1 well reached TD at 8,855' and logged 77' of
  gross and 45' of net oil and natural gas pay from
  two expected productive sands. Drilling of the
  second well began March 22, 2004 and is expected
  to commence production during April. A third well
  will commence after completion of the second
  well. ATP is the operator and has a 51 working
  interest.
• Matagorda Island 709 water depth 88
• The Matagorda Island 709 A-1 ST1 well, TD
  11,325, encountered the proved undeveloped
  reserves that ATP had expected and the well was
  placed on production March 24, 2004. The proved
  reserves in the Miocene Marg "A" sands that ATP
  was expecting amounted to 346' of gross and 113'
  of net natural gas pay. ATP additionally
  encountered a new pay sand with approximately
  152' of gross and 64' of net natural gas pay. ATP
  is the operator with a 62.5 working interest.
  Production is currently curtailed as a result of
  downstream pipeline repairs.
• West Cameron 237 water depth 70
• At West Cameron 237, two wells will be re-entered
  and sidetracked in 2004 to develop proved
  undeveloped reserves from a natural gas reservoir
  at approximately 5,600 TVD and from three other
  reservoirs located between 7,200 and 8,100 TVD.
  ATP is the operator and has a 75 working
  interest.

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Mississippi Canyon 711 (2005 Development)

• Key Features
• MC 711 (Gomez) gross proved reserves gt 100 Bcfe
• Approximately 3,000 water depth
• Six wells encountered hydrocarbons
• four wells re-enterable
• ATP operates with a 99 WI
• 2005 Development Plans
• Re-enter two wells production projected late
  2005
• Future Development Plans
• Re-enter other two wells
• Target other identified reserves

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The Tors (UK) (2006 Development)

• Key Features
• Located in 185 feet of water
• Two wells were tested at 33 MMcf/d and 12 MMcf/d
• Cluster of reservoirs in the North Sea
• ATP operates with a 75 working interest
• Gaz de France owns remaining 25 interest
• Target 2006 first production date

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Converting 247 Bcfe of PUD to PD (2004 2008)
PUD
PUD Sales
PUD to PD
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• Production and Financial Highlights

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Production

• ATP produced 17.1 Bcfe in 2003 (63 natural gas)
• All 2003 production was from the Gulf of Mexico
• ATP expects a substantial increase in 2004
  production from both
  the Gulf of Mexico and the North Sea

100E
Daily Production (MMcfe/d)
2004 Production Contributors
Helvellyn West Cameron 237 1
2 Garden Banks 142 Ship Shoal 358 2
3 Garden Banks 186 West Cameron
101 Matagorda Island 709 Eugene Island
30/71 Ship Shoal 358 1 East Cameron
240 Brazos 544 compression West Cameron
432 Red New 2004 Production
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Development Capital Impact on Production
There is a high correlation between Drilling
CAPEX in one year and Production in the
subsequent year
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2004 Capital Expenditures Budget
Capex Budget by Region
Capex Budget by Type
( in millions)
( in millions)
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Comprehensive Hedging Program
12.3 Bcfe hedged in 2004 at 5.13/Mcfe 3.8 Bcfe
hedged in 2005 at 5.37/Mcfe
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New 185 Million CSFB Senior Term Loan

• Maturity
• Five Year March 2009
• New funds and liquidity
• 56.0 million
• Collateral
• Same as retired facility, substantially all of
  our US and UK oil and gas properties
• Terms
• 150 million LIBOR (floor of 2) 8.50 (9.5
  after 6 months)
• 35 million LIBOR (floor of 2) 10.00
• Warrants - 2.45 million shares at 7.25 for six
  years
• OID 97

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2004 Cash Flows

• New Senior Term Loan
• Sale of approximately 25 interest in 7
  predominantly PUD properties for 19.5 million
• Cash Flow from increased production
• Higher Hedged Prices (5.13/Mcfe in 2004 and
  5.37/Mcfe in 2005)

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• Peer Analysis

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Selected Offshore EP Companies
Red-ATP Peer Comps
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Peer Analysis Proved Reserves
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Peer Analysis SEC PV 10
SEC PV-10 values incorporate future operating
costs, development costs, and price
differentials.
Note Enterprise Value is pro forma announced
2004 capital transactions.
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Peer Analysis Competitive Economics
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Peer Analysis Attractive ATP Equity Upside
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Growth Strategy Summary

• Enhance our attractive PUD inventory
• Improve on already competitive FD costs
• Maintain a proactive hedging program
• Minimum of 40 of PDP production hedged
• Commence MC 711 development plans
• Shoot 3-D seismic survey at Emerald Oil Field
• Better imaging to optimize recovery of oil and
  gas reserves

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Investment Highlights

• Strong liquidity position
• Rapid 2004 production growth
• Successful development track record (97 success
  rate)
• High quality, multi-year development inventory
• Upside potential Emerald, Gomez and The Tors
• ATPs shares provide compelling value

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ATP Oil Gas Corporation (NASDAQ ATPG)
ATP Oil Gas Corporation4600 Post Oak Place,
Suite 200Houston, TX 77027-9726713-622-3311 AT
P Oil Gas (UK) Limited Victoria House, London
Square, Cross Lanes Guildford, Surrey GU1 1UJ
United Kingdom 44 (0) 1483 307200 ATP Oil Gas
(Netherlands) B.V. Water-Staete Gebouw Dokweg 31
(B) 1976 CA IJmuiden The Netherlands 31 (0) 255
523377 www.atpog.com