The largest petroleum company in the world is the Saudi Arabian Oil Company, not Shell, as the original answer stated. The top 10 petroleum companies in the world are as follows according to petrostrategies.org (http://www.petrostrategies.org/Links/Worlds_Largest_Oil_and_Gas_Companies_Sites.htm):
The largest petroleum company in the United States is Exxon/Mobile, which ranks seventeenth in the world.
Seems to be a pretty up to date list of Buyers, Sellers & Refiners below :
Abu Dhabi National Oil Company
BHP Billiton, Australia
BP, United Kingdom
Exxon Mobil
Chevron
ConocoPhillips
Citgo, Venezuela
Gazprom, Russia (Largest Per Barrell Refining in Russia)
Global Energy Swiss AG, ZUG, Swizterland
Gulf Oil, Luxembourg
Iraq National Oil Company
Kuwait Gulf Oil Company, Kuwait
Locstein Petroleum Commodities, Switzerland (Reported Multi Billion Dollar Buying Capabilities)
LUKoil, Russia
Nippon Oil, Japan
Oman Oil Company (OOC), Oman
Petrobras
Petrochina, China (Largest globally)
Petrolos De Venezuela
PETRONAS, Malaysia
Qatar Petroleum, Qatar
Questar, United States of America
Reliance Industries Limited, India
Repsol YPF, Spain ( Largest Spanish End User )
Rosneft, Russia (Second Largest in Russia )
Royal Dutch Shell, Netherlands
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 of America (subsidiary of Royal Dutch Shell
State Oil Company of Azerbaijan, SOCAR Azerbaijan
Sonatrach
Total, France
The British Petroleum(BP) who are responsible for the oil spill but they are still the biggest company regarding the oil spills.
Caspian International Petroleum Company was created in 1996.
BP is owned by BP also known as British Petroleum. It is headquartered in London, England and is the 6th largest oil company in the world.
Galp
the biggest company come from the small company at all.
The biggest petroleum company in Italy is the Eni S.p.A. This is an oil and gas company.
The British Petroleum(BP) who are responsible for the oil spill but they are still the biggest company regarding the oil spills.
Lots of companies drill for petroleum, It's one of the biggest industries in the world.
The Exxon oil company is the biggest petrochemical company in the world.
Studio Ghibli was ranked as the biggest anime company in the world.
The biggest company in the world, by revenue, is Walmart. Walmart's revenue for the 2013 fiscal year was $476 billion. The second biggest company is Royal Dutch Shell, the third is Exxon Mobile Corporation, and the fourth is China National Petroleum Corporation.
bimbo bakeries USA is the biggest company in the world
nokia
Mars
Toyota
Iraq Petroleum Company was created in 1929.
Phillips Petroleum Company was created in 1917.