List of petroleum companies

Ranked list by size.
A list of the largest petroleum companies is always somewhat arbitrary as state-owned companies operate differently to private-owned ones. As of April 2007 here are the list of the biggest petroleum companies in terms of oil reserves, figures in billions of barrels:[1]
Saudi Arabian Oil Company 295
National Iranian Oil Company 287
Qatar Petroleum 165
Abu Dhabi National Oil Company 137
Iraq National Oil Company 137
Gazprom 115
Kuwait Petroleum Corporation 107
Petróleos de Venezuela S.A. 102
Nigeria National Oil Corporation 62
National Oil Corporation (Libya) 45
Sonatrach 40
Rosneft 35

Alphabetical list of companies.

Abu Dhabi National Oil Company (ADNOC), United Arab Emirates
Addax Petroleum, Switzerland
Alon USA, United States
Amerada Hess Corporation, United States
Anadarko Petroleum Corporation, United States
Apache Corporation, United States
Arbusto Energy, United States
Atlantic Petroleum, Faroe Islands
BG Group, United Kingdom
Bharat Petroleum Corporation Limited, India
BHP Billiton, Australia
BP, United Kingdom
Cairn Energy, India
Canadian Natural Resources, Canada
Charottar Gas Sahkari Mandli., India
Chevron Corporation, United States
Citgo, Venezuela
CNOOC Ltd., China
ConocoPhillips, United States
Crown Central Petroleum, United States
Cupet, Cuba
Devon Energy, United States
Ecopetrol, Colombia
Emarat, UAE
Emarat Misr, Egypt
Enbridge, Canada
EnCana, Canada
ENSCO International, United States
Elinoil Hellenic Petroleum Company S.A., Greece
Eni, Italy
Entreprise Tunisienne d'Activites Petroliere (ETAP), Tunisia
Essar Oil, India
ExxonMobil, United States
Faroe Petroleum, Faroe Islands
Galp Energia, Portugal
Gujarat Oleo Chem Ltd., India
Geo Global Resources., India
Petronet LNG Limited, India
Gujarat Gas Co. Ltd., India
Gujarat State Petroleum Corporation, India
Gulf Oil, Luxembourg
Grupa LOTOS, Poland
Hellenic Petroleum, Greece
HOECL, India
Husky Energy, Canada
Imperial Oil, Canada
INA (Industrija Nafte), Croatia
Indian Oil Corporation, India
Insight Energy Corp, United States
Irving Oil, Canada
Jubiliant Empro, India
JHON ENERGY, India
Kerr-McGee, United States
Koch Industries, United States
Kuwait German Petroleum Company, Canada
The Louisiana Land & Exploration Company, United States
LUKoil, Russia
Marathon Oil Corporation, United States
Maxol Group, Republic of Ireland
MedcoEnergi, Indonesia
Mol Group, Hungary
Naftna Industrija Srbije, Serbia
National Iranian Oil Company (NIOC), Iran
National Oil Corporation, Libya
Neste Oil, Finland
North Atlantic Petroleum, Canada
Northern Territory Oil Limited, Australia
NNPC,Nigeria
Occidental Petroleum
Oil & Gas Development Company Limited (OGDCL), Pakistan
Oil & Gas Petroleum Corporation, United States
Oil India Limited, India
OMV, Austria
ONGC, India
PKN Orlen S.A., Poland
PSO, Pakistan
Petróleos de Venezuela, Venezuela
Petroleos Mexicanos, Mexico
Petro-Canada, Canada
Petro Peru, Peru
Petrobras, Brazil
PetroChina, China
Petroconpak, Pakistan
PetroKazakhstan, Canada
Petrom, Romania
Petron Corporation, Philippines
PETRONAS, Malaysia
Petrotrin, Trinidad and Tobago
Pertamina, Indonesia
Piyush Petroleum Co. Ltd, India
Pogo Producing, United States
Polish Oil and Gas Company, Poland
Prize Petroleum CO.LTD., India
Qatar Petroleum, Qatar
Reliance Industries Limited, India
Repsol YPF, Spain
Rompetrol Group N.V., Romania
Royal Dutch Shell, Netherlands, United Kingdom
Santos Limited, Australia
Sasol, South Africa
Saudi Aramco, Saudi Arabia (the largest in the world)
Shell Canada, Canada (subsidiary of Royal Dutch Shell)
Shell Oil Company, United States (subsidiary of Royal Dutch Shell)
Sinclair Oil, United States
Sinopec, China
Sonangol, Angola
Sonatrach, Algeria
SPC, Singapore
StatoilHydro, Norway
State Oil Company of Azerbaijan, SOCAR Azerbaijan
Stuart Petroleum Limited, Australia
Sunoco, United States
Suncor Energy, Canada
Surgutneftegaz, Russia
Syncrude, Canada
Talisman Energy, Canada
Teikoku Oil, Japan
Todd Energy, New Zealand
Total, France
Turkish Petroleum Corporation, Turkey
Turkish Petroleum International Company Limited, Turkey
Tüpraş, Turkey
United Petroleum, Australia
United Refining Company, United States
Vaalco Energy Inc., United States
Van Doren Oil, United States
Wyngate International, Inc. United States
Woodside Petroleum, Australia
YPFB, Bolivia
YUKOS, Russia