O'Neal Resources Corp.
O.I.L. Energy Corp.
Oakmont Corp.
Obow Exploration Inc.
Ocean Energy Inc.
ODG Private Equity Group
ODYSSEY Petroleum Corp.
Officer Basin Energy Inc.
Offshore Development Inc.
OGR 96 Ltd.
Oil & Gas Investment Corp.
Oilexco Inc.
OJSC Tambeyneftegas
Oklahoma Oil & Gas Management Inc.
Olympic Peru
Omimex Petroleum
Onebane, Donohoe, Bernard, Torian
Oneok Inc.
Online Resources
Operations Management Ltd.
Opon Development Co.
Optima Petroleum Corp.
Ore and Petrol Partners LLC.
Orient Petroleum (Central Asia)
Osborne Oil Co.
Overseas Private Investment Corp.
Oxbow Energy Inc.
Oxy USA Inc.
O'Brien Resources LLC.
O'Sullivan Oil & Gas Co. Inc.
Oakland Petroleum
Oaktree Capital Partners
Occidental Petroleum Corp.
Oculus Energy Co.
ODIN Capital Inc.
Oedekoven Water Hot Oil Service
Offset Energy Corp.
Offshore Energy Development Corp.
OGY Petroleum
Oil City Petroleum Inc.
OJSC MMC Norslik Nickel
Old Oak Capital LLC.
Omimex Canada Ltd.
OMV (Pakistan) Exploration GMBH
Oneida and Western Energy Co.
ONGC Videsh Ltd.
Opal Resources LLC.
Opicoil America Ltd.
OPT Inc.
Orbis Energy LLC.
Oregon Natural Gas Development Corp.
Orion Securities Inc.
Output Exploration LLC.
Owen Inc.
Oxy Services Inc.