| 101 | Oasis Petroleum | | Gas Operator | Feb 1984 |
| 102 | Oasis Petroleum North America LLC | Houston, TX 77002 | Oil & Gas Operator | Feb 2025 |
| 103 | Oasis Petroleum Permian LLC | Houston, TX 77002 | Oil & Gas Operator | Apr 2025 |
| 104 | Oasis Production Co., Inc. | | Oil & Gas Operator | Jun 1988 |
| 105 | Oast, Thomas H. | Greenville, NC 27835 | Oil Operator | Nov 1985 |
| 106 | Oates, John Co., Inc. | Stinnett, TX 79083 | Oil & Gas Operator | Apr 2025 |
| 107 | Obax Oil And Gas LLC | Saint Louis, MO 63131 | Oil Operator | Apr 2025 |
| 108 | Obele Oil Corporation | Sedona, AZ 86336-5745 | Oil & Gas Operator | May 2017 |
| 109 | Obele Operating Company LLC | Sedona, AZ 86336-5745 | Oil & Gas Operator | Jan 2025 |
| 110 | Oberlander Leslie A Jake | Covington, OK 73730 | Oil Operator | Jun 2007 |
| 111 | Obermiller Clarence Trust | Creston, OH 44217 | Oil & Gas Operator | Dec 1987 |
| 112 | Obermiller Paul J | Creston, OH 44217 | Oil & Gas Operator | Dec 2014 |
| 113 | Oblaen Resources LLC | Wallis, TX 77485 | Oil & Gas Operator | Apr 2025 |
| 114 | Occ Operating Co. | | Oil & Gas Operator | Apr 2019 |
| 115 | Occidental Energy Company, Inc. | Houston, TX 77282 | Oil & Gas Operator | Jul 2021 |
| 116 | Occidental Energy Marketing, Inc. | Houston, TX 77227 | Gas Operator | Sep 2015 |
| 117 | Occidental Energy MKT Inc | Houston, TX 77001 | Oil & Gas Operator | Jan 2011 |
| 118 | Occidental Of Elk Hills Inc. | | Oil & Gas Operator | Dec 2014 |
| 119 | Occidental Permian LTD. | Houston, TX 77046 | Oil & Gas Operator | Apr 2025 |
| 120 | Occidental Petroleum Corporation | | Oil & Gas Operator | Dec 2021 |
| 121 | Occidental W TX Overthrust, Inc. | Houston, TX 77210 | Oil & Gas Operator | Dec 2021 |
| 122 | Ocean Energy Inc Ndba Devon Louisiana Corp | | Oil & Gas Operator | Jul 2001 |
| 123 | Ocean Energy Resources Inc. | Houston, TX 77002 | Oil & Gas Operator | Dec 2024 |
| 124 | Ocean Energy, Inc. | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 125 | Ocfiw Oil Company, Inc. | Hartington, NE 68739 | Oil & Gas Operator | Dec 2009 |
| 126 | Ochiltree Oil Company | Edmond, OK 73034 | Oil & Gas Operator | Apr 2020 |
| 127 | Oci LLC | Thermopolis, WY 82443 | Oil Operator | Jan 2024 |
| 128 | Octagon Resources Corporation | | Oil Operator | Apr 2005 |
| 129 | Octagon Resources LLC | Norman, OK 73071-1295 | Oil & Gas Operator | May 2015 |
| 130 | Octane Energy Operating, LLC | Midland, TX 79701 | Oil & Gas Operator | Apr 2025 |
| 131 | Odebralski, Michael & Connie | Fredonia, NY 14063 | Gas Operator | Dec 2023 |
| 132 | Odegard Energy, Inc. | Houston, TX 77024 | Oil & Gas Operator | Jul 2020 |
| 133 | Odegard Resources/Omni Exp | Columbus, OH 43207 | Oil & Gas Operator | Sep 1986 |
| 134 | Odell Larry | Oologah, OK 74053 | Oil Operator | Apr 2011 |
| 135 | Oden, Robin H., Inc. | Midland, TX 79702 | Oil & Gas Operator | Apr 1994 |
| 136 | Odessa Exploration, Inc. | Midland, TX 79702 | Oil & Gas Operator | Apr 2025 |
| 137 | Odessa Oil Investment Co., Inc. | Odessa, TX 79762 | Oil & Gas Operator | Nov 2016 |
| 138 | Odom, Claude | | Oil Operator | Jul 1983 |
| 139 | Odom, R. H. | Snyder, TX 79550 | Oil & Gas Operator | Jun 1996 |
| 140 | Odom, Ralph R. | | Oil & Gas Operator | Aug 1993 |
| 141 | Odum Oil & Gas Co. | Harper, TX 78631 | Oil & Gas Operator | Apr 2025 |
| 142 | Odum Ronald L | Garfield, AR 72732 | Oil Operator | Jan 2025 |
| 143 | Ody Oil Corp. | | Oil & Gas Operator | Oct 1994 |
| 144 | Odyssey Operating Company | | Oil & Gas Operator | Sep 2020 |
| 145 | Odyssey Petroleum Company | Houston, TX 77010 | Oil & Gas Operator | Apr 1995 |
| 146 | Odyssey Petroleum Corp. | | Oil & Gas Operator | Jun 2011 |
| 147 | Odyssey Petroleum, Inc. | Overland Park, KS 66282 | Oil & Gas Operator | Apr 2009 |
| 148 | Oedekoven Amerifields Resources LLC | Sugar Land, TX 77478 | Oil Operator | Feb 2025 |
| 149 | Oedekoven Water & Hot Oil | Recluse, WY 82725 | Oil & Gas Operator | Mar 2025 |
| 150 | Oeth DRLG Co | | Oil Operator | Dec 2018 |
| 151 | Oex-1 LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Mar 2024 |
| 152 | Oexco, Inc. | Tulsa, OK 74136 | Oil & Gas Operator | Mar 2015 |
| 153 | Off Broadway Mineral Rights LLC | | Oil & Gas Operator | Oct 2024 |
| 154 | Offield Lease Operations LLC | Wilson, OK 73463 | Oil & Gas Operator | May 2023 |
| 155 | Offset Oil & Gas | Big Spring, TX 79720 | Oil & Gas Operator | Aug 2003 |
| 156 | Offshore Group, Inc. The | Houston, TX 77024 | Oil & Gas Operator | Apr 2025 |
| 157 | Offshore Oil & Gas Inc | Houston, TX 77063 | Oil & Gas Operator | Sep 1994 |
| 158 | Offshore Shelf LLC | | Oil & Gas Operator | Dec 2007 |
| 159 | Ofs-Tulsa Corporation | Fort Worth, TX 76102 | Oil & Gas Operator | Feb 1997 |
| 160 | Oft Inc. | Houston, TX 77079 | Oil & Gas Operator | Apr 2025 |
| 161 | Og Co., Inc. | Houston, TX 77057 | Oil & Gas Operator | Apr 2025 |
| 162 | Oga Operating L.L.C. | Midland, TX 79702 | Oil & Gas Operator | Jan 2000 |
| 163 | Ogden Oil Co., Inc. | | Oil Operator | May 1981 |
| 164 | Ogden Resources Corporation | Bryan, TX 77802 | Oil & Gas Operator | Apr 2025 |
| 165 | Ogden Resources, LTD. | Bryan, TX 77802 | Oil & Gas Operator | Feb 2009 |
| 166 | Ogh Oil Company | | Oil Operator | Sep 1995 |
| 167 | Ogle Petroleum Inc. | | Oil & Gas Operator | Dec 1989 |
| 168 | Oglesby Oil Company | | Oil & Gas Operator | Nov 2023 |
| 169 | Oglesby Prod & Expl Co Inc | | Oil & Gas Operator | Nov 1987 |
| 170 | Oglesby, Marshall | | Oil Operator | May 1990 |
| 171 | Ogog Operating, LLC | Dallas, TX 75367 | Oil & Gas Operator | Apr 2025 |
| 172 | Ogris Operating LLC | | Gas Operator | Jan 2025 |
| 173 | Ogs Operating Company, Inc. | Midland, TX 79701 | Oil & Gas Operator | Sep 2008 |
| 174 | Ogx Operating, LLC | Midland, TX 79702 | Oil & Gas Operator | Apr 2025 |
| 175 | Ogx Resources LLC | Midland, TX 79702 | Oil & Gas Operator | Oct 2011 |
| 176 | Ohio Energy Assets, Inc. | Laurelville, OH 43135 | Oil & Gas Operator | Dec 2014 |
| 177 | Ohio Energy Group Inc | Uniontown, OH 44685 | Oil & Gas Operator | Dec 1988 |
| 178 | Ohio Energy Operators LLC | Colorado Spring, CO 80908 | Oil Operator | Dec 2018 |
| 179 | Ohio Investment Leas Inc | Danville, OH 43014 | Oil & Gas Operator | Dec 1989 |
| 180 | Ohio Kentucky Oil Corporation | Lexington, KY 40503 | Oil & Gas Operator | Dec 2023 |
| 181 | Ohio L & M Company Inc | Marietta, OH 45750 | Oil & Gas Operator | Dec 2008 |
| 182 | Ohio Natural Fuel Co | Canton, OH 44718 | Oil & Gas Operator | Dec 1985 |
| 183 | Ohio Oil & Gas | Fowler, OH 44418 | Oil & Gas Operator | Dec 1988 |
| 184 | Ohio Production Corp | Westerville, OH 43081 | Oil & Gas Operator | Dec 2001 |
| 185 | Ohio Production* | Newark, OH 43055 | Oil & Gas Operator | Dec 1987 |
| 186 | Ohio Valley Energy Systems Corp | Austintown, OH 44515 | Oil & Gas Operator | Dec 2024 |
| 187 | Ohio Valley Energy, Inc | Livermore, KY 42352 | Oil Operator | Dec 2023 |
| 188 | Ohlhausen Oil Company | Abilene, TX 79608 | Oil & Gas Operator | Apr 2025 |
| 189 | Oi Auburn, Inc. | Tulsa, OK 74135 | Gas Operator | Dec 2023 |
| 190 | Oil & Gas Acquisition Group, Inc | Austin, TX 78716 | Oil & Gas Operator | May 2003 |
| 191 | Oil & Gas Development Company | | Oil & Gas Operator | May 1991 |
| 192 | Oil & Gas Exploration Inc | Cleveland, OK 74020 | Oil & Gas Operator | Aug 2013 |
| 193 | Oil & Gas MGMT Inc | Mount Pleasant, PA 15666-3304 | Oil & Gas Operator | Dec 2024 |
| 194 | Oil & Gas Operations | Midland, TX 79706 | Oil & Gas Operator | Apr 2025 |
| 195 | Oil & Gas Producers, Inc. | Topeka, KS 66604 | Oil Operator | Jun 2004 |
| 196 | Oil & Gas Properties | Midland, TX 79704 | Oil & Gas Operator | Apr 2025 |
| 197 | Oil & Gas Property MGMT., Inc. | Dallas, TX 75201 | Oil & Gas Operator | Jul 1996 |
| 198 | Oil & Gas Servic | | Oil Operator | Jun 1983 |
| 199 | Oil & Gas Solutions LTD | Wooster, OH 44691 | Oil & Gas Operator | Dec 2007 |
| 200 | Oil & Gas SVC Inc | Reelsville, IN 46171-9686 | Gas Operator | Dec 1991 |