| 101 | United Investment Group | | Oil Operator | Nov 2004 |
| 102 | United Meridian | | Oil Operator | Dec 1992 |
| 103 | United Natural Gas LLC | Denver, CO 80202 | Oil & Gas Operator | Feb 2020 |
| 104 | United Natural Resources Corp | | Oil Operator | Jan 1986 |
| 105 | United O&G/Atlee Miller | Millersburg, OH 44654 | Oil & Gas Operator | Dec 1985 |
| 106 | United Oil & Gas | | Oil Operator | Feb 1988 |
| 107 | United Oil & Minerals L. P. | Austin, TX 78746 | Oil & Gas Operator | Jun 2003 |
| 108 | United Oil & Minerals, Inc. | Austin, TX 78746 | Oil & Gas Operator | Jan 2001 |
| 109 | United Oil Corporation | Denver, CO 80202-3813 | Oil & Gas Operator | Jan 2024 |
| 110 | United Operating Company | Olney, TX 76374 | Oil & Gas Operator | Aug 2003 |
| 111 | United Operating, LLC *** | Midland, TX 79710 | Oil & Gas Operator | Apr 2024 |
| 112 | United Operators, Inc. | | Oil Operator | Sep 1999 |
| 113 | United Petro LTD. | | Oil & Gas Operator | Dec 2018 |
| 114 | United Petroleum | | Oil Operator | Mar 1986 |
| 115 | United Petroleum & Gas, Inc. | Kilgore, TX 75663 | Oil & Gas Operator | Apr 2024 |
| 116 | United Petroleum Corporation | Edgwater, CO 80214 | Oil & Gas Operator | May 1996 |
| 117 | United Petroleum Technologies | Hondo, TX 78861 | Oil & Gas Operator | Aug 2001 |
| 118 | United Primary Resources Inc | Milton, WA 98354-9361 | Oil & Gas Operator | Feb 2016 |
| 119 | United Producers Inc | Broken Arrow, OK 74012-8247 | Oil & Gas Operator | Mar 2020 |
| 120 | United Producing Co Inc | | Oil & Gas Operator | May 1961 |
| 121 | United Production Company LLC | Edmond, OK 73083-5348 | Oil & Gas Operator | Feb 2024 |
| 122 | United Reserve G | | Oil Operator | Aug 1987 |
| 123 | United Resources Corp | Olean, NY 14760 | Oil & Gas Operator | Dec 2020 |
| 124 | United Resources LP | Austin, TX 78746 | Oil & Gas Operator | Oct 2011 |
| 125 | United Resources LP A Texas LMTD PRNTSHP | Austin, TX 78746 | Oil & Gas Operator | Sep 2003 |
| 126 | United Security Associates Inc | | Oil & Gas Operator | Dec 2020 |
| 127 | United Southern Resources Inc. | | Gas Operator | Nov 2013 |
| 128 | United States Energy Corp. | Longview, TX 75601 | Oil & Gas Operator | Feb 2024 |
| 129 | United States Exploration, Inc. | Denver, CO 80802 | Oil & Gas Operator | Jun 2009 |
| 130 | United States Gypsum Company | Oakfield, NY 14125 | Oil & Gas Operator | Dec 2022 |
| 131 | United States Trading & Trans | Dallas, TX 75380-3342 | Oil & Gas Operator | Dec 1994 |
| 132 | United Texas Oil LLC | Houston, TX 77027 | Oil & Gas Operator | Apr 2024 |
| 133 | United Texas Petroleum Inc. | McKinney, TX 75070 | Oil & Gas Operator | Apr 2024 |
| 134 | United Utilities Corporation | Conroe, TX 77301 | Oil & Gas Operator | Oct 1998 |
| 135 | United Well Completion, Inc | Corbin, KY 40701 | Oil & Gas Operator | Dec 2022 |
| 136 | United World Energy Corporation | | Oil & Gas Operator | Jan 2024 |
| 137 | United World Energy, Inc. | Aurora, CO 80040 | Oil & Gas Operator | Apr 2024 |
| 138 | Unitex Oil & Gas, L.L.C. | Midland, TX 79701 | Oil & Gas Operator | Apr 2024 |
| 139 | Unity Petroleum | Howard, OH 43028 | Oil & Gas Operator | Dec 2021 |
| 140 | Universal Cyclops Specialty Steel Div | Pittsburgh, PA 15228-2702 | Gas Operator | Dec 1985 |
| 141 | Universal Drilling Co., Inc. | Denver, CO 80203 | Oil & Gas Operator | Sep 2003 |
| 142 | Universal Exploration Inc | Wadsworth, OH 44281-9460-9460 | Oil & Gas Operator | Feb 2012 |
| 143 | Universal Fuels Company | | Oil & Gas Operator | Oct 1993 |
| 144 | Universal Geopower LLC | Houston, TX 77057 | Oil & Gas Operator | May 2016 |
| 145 | Universal Land | | Oil Operator | Dec 2023 |
| 146 | Universal Oil Co. | | Oil Operator | Nov 2023 |
| 147 | Universal Operating, Inc | Evansville, IN 47715 | Oil & Gas Operator | Dec 2022 |
| 148 | Universal Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Sep 2002 |
| 149 | Universal Producers, Inc. | | Oil Operator | Jun 2001 |
| 150 | Universal Resour | | Oil & Gas Operator | Dec 1996 |
| 151 | Universal Resources Corp. | Salt Lake Cty, UT 84145 | Oil & Gas Operator | Jan 2000 |
| 152 | Universal Resources Holdings Inc | Dunkirk, NY 14048 | Oil & Gas Operator | Dec 2022 |
| 153 | University Field Management LLC | | Oil Operator | Nov 2023 |
| 154 | Unknown | Houston, TX 77208 | Oil & Gas Operator | Dec 2022 |
| 155 | Unknown Owner | Columbus, OH 43229 | Oil & Gas Operator | Dec 2008 |
| 156 | Unocal Explor. Corp. | | Oil & Gas Operator | Nov 1990 |
| 157 | Unocal Exploration Corporation | Houston, TX 77001 | Oil & Gas Operator | May 1992 |
| 158 | Unoso Operating Company L.L.C. | Georgetown, TX 78633 | Oil & Gas Operator | Apr 2024 |
| 159 | Unrein Oil Co | | Oil Operator | Dec 2023 |
| 160 | Unruh, Elmer | Galva, KS 67443 | Oil & Gas Operator | Aug 1998 |
| 161 | Unruh, Mark D. | Peru, KS 67360 | Oil Operator | Sep 2011 |
| 162 | Unswept Oil Company | Corsicana, TX 75151 | Oil & Gas Operator | Jan 2018 |
| 163 | Untener Bishop Kenneth (Diocese Of Saginaw) | | Oil Operator | Dec 2023 |
| 164 | Uosi Operating, Inc. | Lovelady, TX 75851 | Oil & Gas Operator | Apr 2024 |
| 165 | Upcurve Energy, LLC | Houston, TX 77024 | Oil & Gas Operator | Apr 2024 |
| 166 | Upda Operators, Inc. | Jacksboro, TX 76458 | Oil & Gas Operator | Dec 2009 |
| 167 | Updike Resources Inc | Newcastle, WY 82701 | Oil & Gas Operator | Jun 1998 |
| 168 | Upham Oil & Gas Company | Mineral Wells, TX 76068 | Oil & Gas Operator | Apr 2024 |
| 169 | Upham, Chester R., Jr. | Mineral Wells, TX 76067 | Oil & Gas Operator | Aug 2001 |
| 170 | Upland Exploration LLC | | Oil & Gas Operator | Feb 2024 |
| 171 | Upland Operating, LLC | Dallas, TX 75226 | Oil & Gas Operator | Apr 2024 |
| 172 | Upland Production Company | Edmond, OK 73083 | Oil & Gas Operator | Apr 2024 |
| 173 | Upland Resources | | Oil Operator | Jul 1983 |
| 174 | Upland Resources LLC | Canadian, TX 79014 | Oil & Gas Operator | Apr 2024 |
| 175 | Upland Resources, Inc. | Canadian, TX 79014 | Oil & Gas Operator | Dec 2009 |
| 176 | Uplands Resources Inc | Tulsa, OK 74103-4141 | Oil & Gas Operator | Jan 2024 |
| 177 | Uplift Production Company, Inc. | Shamrock, TX 79079 | Oil & Gas Operator | Feb 1999 |
| 178 | Upp Operating, LLC | Houston, TX 77002 | Oil & Gas Operator | Apr 2024 |
| 179 | Upstream Exploration LLC | Metairie, LA 70002 | Oil & Gas Operator | Jan 2020 |
| 180 | Upstream Properties, LLC | Southlake, TX 76092 | Oil & Gas Operator | Apr 2024 |
| 181 | Upstream Resource Partners, LLC | Palestine, TX 75803 | Oil Operator | Apr 2024 |
| 182 | Uptex Operating Inc. | Dallas, TX 75201 | Oil & Gas Operator | May 2011 |
| 183 | Uptex Operating, L.P. | Dallas, TX 75201 | Oil & Gas Operator | May 2010 |
| 184 | Upton Resources U.S.A. Inc. | | Oil & Gas Operator | Oct 2013 |
| 185 | Uranus, Inc. | Kansas City, MO 64112 | Oil Operator | Jan 2000 |
| 186 | Urban Oil & Gas Group, LLC | Plano, TX 75074 | Oil & Gas Operator | Apr 2024 |
| 187 | Urroz Oil & Gas LLC | Evanston, WY 82931 | Oil & Gas Operator | Jun 2020 |
| 188 | Ursa Major (Crow Og), LLC | Billings, MT 59101 | Gas Operator | Aug 2017 |
| 189 | Ursa Operating Company LLC | Denver, CO 80265 | Oil & Gas Operator | Dec 2020 |
| 190 | Ursus Oil And Gas | Tyler, TX 75703 | Oil & Gas Operator | Apr 2024 |
| 191 | Us Ecology Winnie, LLC | Winnie, TX 77665 | Oil Operator | Apr 2024 |
| 192 | Us Energy Corp. | Houston, TX 77057 | Oil & Gas Operator | Dec 2021 |
| 193 | Us Energy Dev Corp | Getzville, NY 14068-1558 | Oil & Gas Operator | Dec 2021 |
| 194 | Us Energy Exploration Corp | Rural Valley, PA 16249 | Oil & Gas Operator | Dec 2023 |
| 195 | Us Energy Holdings, LLC | Richardson, TX 75080 | Oil & Gas Operator | Apr 2024 |
| 196 | Us Energy Oh LLC | Rural Valley, PA 16249 | Oil & Gas Operator | Dec 2023 |
| 197 | Us Gypsum Co | Oakfield, NY 14125-9722 | Gas Operator | Dec 2005 |
| 198 | Us Liquids Of La, LTD | | Oil Operator | Jun 2002 |
| 199 | Us Oil & Gas Inc | Marietta, OH 45750 | Oil & Gas Operator | Feb 2024 |
| 200 | Us Oil Resources LLC | Lakewood, CO 80123 | Oil Operator | Dec 2023 |