| 101 | Old Dominion Oil Corporation | Oklahoma City, OK 73107 | Oil & Gas Operator | Apr 2009 |
| 102 | Ole Crow Operating | Wichita Falls, TX 76308 | Oil Operator | Dec 2024 |
| 103 | Oleum Incorporated | | Oil & Gas Operator | Mar 1996 |
| 104 | Olia Oil & Gas Services LLC | Cedar Park, TX 78630-2049 | Oil & Gas Operator | Aug 2022 |
| 105 | Oliphant Gertrud | Holdenville, OK 74848-0849 | Oil Operator | Aug 2013 |
| 106 | Oliphant Operating LTD LLC | Tulsa, OK 74159-4529 | Oil Operator | Dec 2024 |
| 107 | Olive Oil & Gas Inc | Jennings, OK 74038 | Oil & Gas Operator | Nov 2024 |
| 108 | Olympia Oil Inc | Edmond, OK 73083-7088 | Oil & Gas Operator | Jul 2020 |
| 109 | Olympic Petroleum Company | Tulsa, OK 74114 | Oil & Gas Operator | Jun 1998 |
| 110 | Omega Energy, LLC | Corpus Chrsti, TX 78418 | Oil & Gas Operator | Mar 2025 |
| 111 | Omimex International Corp | Fort Worth, TX 76103-2300 | Oil & Gas Operator | Dec 2024 |
| 112 | Omimex Petroleum Inc | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2022 |
| 113 | Omni Oil & Gas, Inc. | San Antonio, TX 78229 | Oil & Gas Operator | Oct 2017 |
| 114 | On-Line Oil Inc | Oklahoma City, OK 73105-5208 | Oil & Gas Operator | Mar 2015 |
| 115 | Onapa Gas Company LLC | Tulsa, OK 74136-7253 | Gas Operator | Nov 2019 |
| 116 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 117 | Oneok Field Services Company | Tulsa, OK 74103 | Oil & Gas Operator | Jul 2022 |
| 118 | Oneok Gas Processing LLC | Tulsa, OK 74103 | Oil & Gas Operator | May 2018 |
| 119 | Oneok Gas Transportation Co | Tulsa, OK 74121-2089 | Oil & Gas Operator | Oct 2014 |
| 120 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 121 | Onpoint Oil & Gas LLC | Oklahoma City, OK 73170-4848 | Oil & Gas Operator | Dec 2024 |
| 122 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Jan 2025 |
| 123 | Onyx Energy Corporation | Oklahoma City, OK 73157 | Oil & Gas Operator | May 1994 |
| 124 | Onyx Properties Corp | Oklahoma City, OK 73114 | Oil & Gas Operator | May 2006 |
| 125 | Opal Operating Company LLC | Oklahoma City, OK 73142 | Oil & Gas Operator | Mar 2025 |
| 126 | Open Door Holdings Inc | Surprise, AZ 85387-2015 | Oil & Gas Operator | Feb 2024 |
| 127 | Open Door Productions Inc | Muskogee, OK 74401-1032 | Oil & Gas Operator | Apr 2020 |
| 128 | Open Range Energy LLC | Jones, OK 73049-8744 | Oil & Gas Operator | Nov 2024 |
| 129 | Optima Exploration LLC | Tulsa, OK 74116-5664 | Oil & Gas Operator | Mar 2015 |
| 130 | Opubco Resources Of TX Inc | Dallas, TX 75231 | Oil & Gas Operator | Sep 2005 |
| 131 | Oracle Resources Oklahoma LP | Dallas, TX 75240-5751 | Oil & Gas Operator | Feb 2008 |
| 132 | Orason Resources Inc | Tulsa, OK 74169-1225 | Oil & Gas Operator | Nov 2006 |
| 133 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Jan 2025 |
| 134 | Oren Stone | Erick, OK 73645-4542 | Gas Operator | Jun 2022 |
| 135 | Orion Exploration LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Apr 2015 |
| 136 | Orion Exploration Partners LLC | Tulsa, OK 74105-5153 | Oil & Gas Operator | Dec 2024 |
| 137 | Orloski John C | Bartlesville, OK 74006 | Oil & Gas Operator | Dec 2024 |
| 138 | Oryx Crude Trading & Transporation LP | Dallas, TX 75221 | Oil & Gas Operator | Jun 1999 |
| 139 | Osa Oil & Gas LLC | Tulsa, OK 74131 | Oil & Gas Operator | Aug 2023 |
| 140 | Osage Energy LLC | Colony, KS 66015 | Oil Operator | Nov 2023 |
| 141 | Osage Energy Resources LLC | Bartlesville, OK 74005-2527 | Oil & Gas Operator | Dec 2024 |
| 142 | Osage Exploration & Development Inc | San Diego, CA 92131-3807 | Oil & Gas Operator | Oct 2016 |
| 143 | Osage Oil & Transportation Inc | Cleveland, OK 74020 | Oil & Gas Operator | Nov 2000 |
| 144 | Osage Operating | Virginia Beach, VA 23452 | Oil & Gas Operator | Oct 2003 |
| 145 | Osage Petroleum Corporation | Saint Louis, MO 63131-4691 | Oil & Gas Operator | Mar 2009 |
| 146 | Osborn Heirs Co | San Antonio, TX 78217 | Oil & Gas Operator | Jan 2025 |
| 147 | Osburn Gerald Dba Ozzy & Son Oil & Gas | Drumright, OK 74030-5467 | Oil Operator | Oct 2020 |
| 148 | Oscar'S Well Service Inc | Okemah, OK 74859 | Oil & Gas Operator | Apr 1998 |
| 149 | Oshtah Oil Company LLC | Stratford, OK 74872 | Oil & Gas Operator | Sep 2018 |
| 150 | Oso Resources LLC | Oklahoma City, OK 73118-5022 | Oil & Gas Operator | Dec 2024 |
| 151 | Osterhout Phillip L | Drumright, OK 74030-0693 | Oil & Gas Operator | Jan 2014 |
| 152 | Oswego Arbuckle Enterprise Inc | S Coffeyville, OK 74072-9702 | Oil & Gas Operator | Mar 2015 |
| 153 | Otc Investors Inc | Locust Grove, OK 74352 | Oil Operator | Sep 2024 |
| 154 | Otc Petroleum Corporation | Nichols Hill, OK 73116 | Oil & Gas Operator | Mar 2015 |
| 155 | Otc/Occ Not Assigned | | Oil & Gas Operator | Dec 2024 |
| 156 | Ouachita Exploration Inc | Chickasha, OK 73018 | Oil & Gas Operator | Dec 2024 |
| 157 | Outback Petroleum Inc | Moore, OK 73160-9998 | Oil & Gas Operator | Mar 2015 |
| 158 | Outlaw Oil And Gas LLC | Kaw City, OK 74641 | Oil & Gas Operator | Dec 2024 |
| 159 | Ovation Energy II, LP | Houston, TX 77279 | Oil & Gas Operator | Jun 2011 |
| 160 | Ovation Energy, LP | N Richlnd HLS, TX 76180 | Oil & Gas Operator | Sep 2004 |
| 161 | Overflow Energy Stack LLC | Booker, TX 79005 | Oil Operator | Sep 2022 |
| 162 | Overflow Energy, LLC | Booker, TX 79005 | Oil & Gas Operator | Mar 2025 |
| 163 | Overland Investments Inc | Coweta, OK 74429 | Oil & Gas Operator | Dec 2024 |
| 164 | Ovintiv Mid-Continent Inc. | The Woodlands, TX 77380-2764 | Oil & Gas Operator | Jan 2025 |
| 165 | Ovintiv USA Inc. | Denver, CO 80202 | Oil & Gas Operator | Mar 2025 |
| 166 | Owens James W | Tulsa, OK 74114-1425 | Oil & Gas Operator | Oct 2022 |
| 167 | Owl Creek Production Co., Inc. | Houston, TX 77027 | Oil & Gas Operator | Apr 2006 |
| 168 | Oxco LLC | Pawhuska, OK 74056 | Oil & Gas Operator | Feb 2015 |
| 169 | Oxford Exploration Company | Denver, CO 80237 | Oil & Gas Operator | Aug 1995 |
| 170 | Oxford Oil Inc | Cleveland, OK 74020 | Oil & Gas Operator | Feb 1997 |
| 171 | Oxley Energy LLC | Houston, TX 77042 | Gas Operator | Jan 2025 |
| 172 | Oxley John C | Tulsa, OK 74103 | Oil & Gas Operator | Sep 1996 |
| 173 | Oxley Petroleum | Tulsa, OK 74119-3609 | Oil & Gas Operator | Jan 2020 |
| 174 | Oxley Petroleum Co | Oklahoma City, OK 73118-1044 | Oil & Gas Operator | Sep 2017 |
| 175 | Oxy USA Inc | Houston, TX 77046 | Oil & Gas Operator | Mar 2025 |
| 176 | Ozark Gas Gathering LLC | Fort Smith, AR 72916 | Oil & Gas Operator | Dec 2024 |
| 177 | Ozark Oil Corporation | Springfield, MO 65804 | Oil & Gas Operator | Oct 1992 |