APA

O'Keefe W., American Petroleum Institute A., World Petroleum Congress (15th. : 1997 : Beijing) & American Petroleum Institute A.The petroleum industry's global commitment to the environment. : .

Chicago

O'Keefe W.F, American Petroleum Institute API, World Petroleum Congress (15th. : 1997 : Beijing) and American Petroleum Institute API.The petroleum industry's global commitment to the environment. : .

Harvard

O'Keefe W., American Petroleum Institute A., World Petroleum Congress (15th. : 1997 : Beijing) and American Petroleum Institute A.The petroleum industry's global commitment to the environment. : .

MLA

O'Keefe W.F, American Petroleum Institute API, World Petroleum Congress (15th. : 1997 : Beijing) and American Petroleum Institute API.: . .