| 101 | Ojai Oil Company | Camarillo, CA 93012 | Oil & Gas Operator | Dec 2024 |
| 102 | Ojb, Inc. | Buda, TX 78610 | Oil & Gas Operator | Mar 2013 |
| 103 | Ojt, LLC | Richmond, TX 77469 | Oil Operator | Mar 2025 |
| 104 | Ok Arena Operating Company | Oklahoma City, OK 73101 | Oil & Gas Operator | Mar 2025 |
| 105 | Ok Oil Company, Inc. | Bivins, TX 75555 | Oil & Gas Operator | Feb 2013 |
| 106 | Okie Crude Company | Tulsa, OK 74103 | Oil & Gas Operator | Dec 2024 |
| 107 | Okie Operating Company, LTD. | Tulsa, OK 74103 | Oil & Gas Operator | Mar 2025 |
| 108 | Okla. Magic Circle Energy Corp. | Shawnee, OK 74801 | Oil & Gas Operator | Jul 2004 |
| 109 | Oklahoma & Northwestern Co. | Oklahoma City, OK 73102 | Oil & Gas Operator | Jan 1997 |
| 110 | Oklahoma Arrowhead Energy, Inc. | Nichols Hill, OK 73116 | Oil & Gas Operator | Sep 1996 |
| 111 | Oklahoma Ea II, L.L.C. | Oklahoma City, OK 73102 | Oil & Gas Operator | Dec 2004 |
| 112 | Oklahoma Marlin Oil Corporation | Oklahoma City, OK 73113 | Oil & Gas Operator | Feb 2020 |
| 113 | Oklahoma Oil Company | Dallas, TX 75206 | Oil & Gas Operator | Aug 2013 |
| 114 | Oklahoma Operating Company | Midland, TX 79708 | Oil & Gas Operator | Mar 2025 |
| 115 | Oklahoma Operating, LLC | Holliday, TX 76366 | Oil Operator | Nov 2003 |
| 116 | Oklahoma Petroleum Allies LLC | Ardmore, OK 73401 | Oil Operator | Oct 2023 |
| 117 | Oklahoma RB Operating Company | Midland, TX 79701 | Oil & Gas Operator | Jan 1998 |
| 118 | Oklahoma Sterling Oil & Gas Corp | Tulsa, OK 74170 | Oil & Gas Operator | Jun 1997 |
| 119 | Oklatex Energy, Inc. | Beaumont, TX 77702 | Oil Operator | Mar 2025 |
| 120 | Okmar Oil Company | Marietta, OH 45750 | Oil & Gas Operator | Jun 2005 |
| 121 | Okreek Oil Company | Weatherford, TX 76086 | Oil & Gas Operator | Mar 2025 |
| 122 | Okt Resources, LLC | Edmond, OK 73013 | Oil & Gas Operator | Mar 2025 |
| 123 | Oky Investments, Inc. | Edmond, OK 73013 | Oil & Gas Operator | Sep 2021 |
| 124 | Ol' Boys Operations LLC | Pampa, TX 79065 | Oil & Gas Operator | Mar 2025 |
| 125 | Old Cedron, L.L.C. | Lubbock, TX 79410 | Oil & Gas Operator | May 2004 |
| 126 | Old Chief Oil, LLC | San Antonio, TX 78205 | Oil Operator | Mar 2025 |
| 127 | Old Pine Energy Corporation | Austin, TX 78755 | Oil Operator | Mar 2025 |
| 128 | Old Timers Oil | Saratoga, TX 77585 | Oil & Gas Operator | Nov 2014 |
| 129 | Old Timers Oil Company, LLC | Saratoga, TX 77585 | Oil Operator | Aug 2022 |
| 130 | Old Timers Oil No. 2 Incorporated | Saratoga, TX 77585 | Oil Operator | Mar 2025 |
| 131 | Old Union Operating Company | Austin, TX 78716 | Oil & Gas Operator | Mar 2025 |
| 132 | Older Than Dirt LLC | Palo Pinto, TX 76484 | Oil & Gas Operator | Mar 2025 |
| 133 | Oldfield Acquisition LP | Austin, TX 78733 | Oil & Gas Operator | Sep 1996 |
| 134 | Ole Chaparral On Possum Kingdom | Wichita Falls, TX 76307 | Oil & Gas Operator | Dec 1997 |
| 135 | Ole, Inc. | Graham, TX 76450 | Oil & Gas Operator | Aug 2003 |
| 136 | Oleum Exploration, LLC | Brodheadsvill, PA 18322 | Oil & Gas Operator | Mar 2023 |
| 137 | Oleum Operating Company, L.C. | Longview, TX 75606 | Oil & Gas Operator | Dec 2021 |
| 138 | Oleum Partners, LLC | Frisco, TX 75034 | Oil & Gas Operator | Mar 2025 |
| 139 | Olifant Energy LLC | Tulsa, OK 74119 | Oil & Gas Operator | Jun 2019 |
| 140 | Olipdp II, LLC | Lafayette, LA 70503 | Oil & Gas Operator | Mar 2025 |
| 141 | Oliver Oil & Gas | Midland, TX 79702 | Oil & Gas Operator | Mar 2025 |
| 142 | Olmos Partners, Inc. | Boerne, TX 78006 | Oil & Gas Operator | Mar 2025 |
| 143 | Olney Oil LLC | Boerne, TX 78006 | Oil Operator | Mar 2025 |
| 144 | Olney Properties, Inc. | Wichita Falls, TX 76307 | Oil & Gas Operator | Sep 2003 |
| 145 | Olsan Brothers, Inc. | Dallas, TX 75251 | Oil & Gas Operator | Apr 1994 |
| 146 | Olsen Energy Inc. | Boerne, TX 78006 | Oil & Gas Operator | Mar 2025 |
| 147 | Olson, S. A. | Kenedy, TX 78119 | Oil & Gas Operator | Aug 1994 |
| 148 | Oltex Production | Idalou, TX 79329 | Oil & Gas Operator | Mar 2025 |
| 149 | Omar Operating Company | Midland, TX 79702 | Oil & Gas Operator | Sep 2013 |
| 150 | Omber Petroleum & Energy Corp. | New Braunfels, TX 78131 | Oil & Gas Operator | Mar 2025 |
| 151 | Omega Alpha Resources, LLC | Dallas, TX 75219 | Oil Operator | Mar 2025 |
| 152 | Omega Energy Corp. | Graham, TX 76450 | Oil & Gas Operator | Mar 2025 |
| 153 | Omega Energy, LLC | Corpus Chrsti, TX 78418 | Oil & Gas Operator | Mar 2025 |
| 154 | Omega Operating, Inc. | Odessa, TX 79769 | Oil & Gas Operator | Mar 2001 |
| 155 | Omimex Energy, Inc. | Fort Worth, TX 76120 | Oil & Gas Operator | Dec 2024 |
| 156 | Omimex Petroleum Inc | Fort Worth, TX 76120 | Oil & Gas Operator | Aug 2022 |
| 157 | Omni E & P, Inc. | San Antonio, TX 78229 | Oil Operator | Apr 2010 |
| 158 | Omni Oil & Gas, Inc. | San Antonio, TX 78229 | Oil & Gas Operator | Oct 2017 |
| 159 | Omni Operating Company(A) | Dallas, TX 75370 | Oil & Gas Operator | Mar 2025 |
| 160 | Omni Petroleum Corporation | Austin, TX 78738 | Oil & Gas Operator | Mar 2025 |
| 161 | On Pointe Operating LLC | Jones, OK 73049 | Oil & Gas Operator | Mar 2025 |
| 162 | Onaroll Operating LLC | Levelland, TX 79336 | Oil Operator | Mar 2025 |
| 163 | One Epoch Energy, Inc. | Abilene, TX 79604 | Oil & Gas Operator | Mar 2008 |
| 164 | One Nickel Operating LLC | Westbrook, TX 79565 | Oil Operator | Mar 2025 |
| 165 | One Tec Operating, LLC | Houston, TX 77002 | Oil & Gas Operator | Nov 2007 |
| 166 | One World Operating, LLC | Tampa, FL 33602 | Oil & Gas Operator | Mar 2025 |
| 167 | Oneok Exploration Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 168 | Oneok Resources Company | Tulsa, OK 74102 | Oil & Gas Operator | Feb 2017 |
| 169 | Onshore Royalties LLC | Houston, TX 77269 | Oil & Gas Operator | Jan 2025 |
| 170 | Onyx Industries LTD, Inc. | Wichita Falls, TX 76308 | Oil & Gas Operator | Aug 2003 |
| 171 | Onyx Producing Company, Inc. | Pampa, TX 79066 | Oil & Gas Operator | Mar 2008 |
| 172 | Opal Energy, Inc. | Katy, TX 77494 | Oil & Gas Operator | Jun 2009 |
| 173 | Opal Operating Company LLC | Oklahoma City, OK 73142 | Oil & Gas Operator | Mar 2025 |
| 174 | Opal Resources Operating Co.,LLC | Cypress, TX 77429 | Oil & Gas Operator | Jan 2019 |
| 175 | Opco Oil & Gas Co. | Dallas, TX 75231 | Oil & Gas Operator | Aug 2003 |
| 176 | Opex Energy, LLC | Houston, TX 77042 | Oil & Gas Operator | Mar 2008 |
| 177 | Opmi Operating Company | Houston, TX 77057 | Oil & Gas Operator | Jun 2008 |
| 178 | Ops Group Limited | Houston, TX 77060 | Oil & Gas Operator | Jun 2014 |
| 179 | Optimum Exploration LLC | Dallas, TX 75240 | Oil & Gas Operator | Mar 2025 |
| 180 | Orange Petroleum Co. | Orangefield, TX 77639 | Oil & Gas Operator | May 1995 |
| 181 | Orangefield Operating Corporation | Dallas, TX 75382 | Oil Operator | Mar 2025 |
| 182 | Orbis Energy, L.L.C. | Austin, TX 78746 | Oil & Gas Operator | Oct 2001 |
| 183 | Orbit Crude, Inc. | Midland, TX 79710 | Oil & Gas Operator | Mar 2025 |
| 184 | Orbit Enterprises, Inc. | Lovington, NM 88260 | Oil & Gas Operator | Mar 2015 |
| 185 | Orbitron Operating Corp. | Fort Worth, TX 76102 | Oil & Gas Operator | Dec 1995 |
| 186 | Orca Operating Company LLC | Houston, TX 77056 | Oil & Gas Operator | Jan 2025 |
| 187 | Origin Prod Co Gonzales Prop LLC | New Braunfels, TX 78132 | Oil & Gas Operator | Mar 2025 |
| 188 | Origin Production Company, Inc. | New Braunfels, TX 78132 | Oil & Gas Operator | Mar 2025 |
| 189 | Origin Production Group LLC | Luling, TX 78648 | Oil Operator | Mar 2025 |
| 190 | Oringderff, Alma Oil Properties | Dallas, TX 75225 | Oil & Gas Operator | Mar 2012 |
| 191 | Oriole Operating LLC | Wichita Falls, TX 76308 | Oil Operator | Mar 2025 |
| 192 | Orion Energen Inc. | Austin, TX 78731 | Oil & Gas Operator | Jul 2023 |
| 193 | Orion Oil & Gas Properties | Amarillo, TX 79109 | Gas Operator | Oct 2000 |
| 194 | Orion Oil & Gas, LLC | Houston, TX 77042 | Oil & Gas Operator | Oct 2007 |
| 195 | Orion Oil And Gas Corporation | Houston, TX 77082 | Oil & Gas Operator | Mar 2025 |
| 196 | Orisol Oil Co. | Houston, TX 77206 | Oil Operator | Jun 2000 |
| 197 | Orla Petco, Inc. | Midland, TX 79702 | Oil & Gas Operator | Mar 2025 |
| 198 | Orland Oil & Gas LLC | FT Lauderdale, FL 33305 | Oil Operator | Mar 2025 |
| 199 | Ormand, Don R. | Midland, TX 79705 | Oil & Gas Operator | Jan 2016 |
| 200 | Oro Resources, LLC | Dallas, TX 75219 | Oil & Gas Operator | Mar 2025 |