| 30301 | U-N-I Exploratio | | Oil & Gas Operator | Dec 1990 |
| 30302 | U-N-I Exploration & Development, Inc. | Yates Center, KS 66783 | Oil & Gas Operator | Jan 2003 |
| 30303 | U. D. Man, Inc. | San Antonio, TX 78212 | Oil & Gas Operator | Jul 2025 |
| 30304 | U. O. C., Inc. | | Oil Operator | Jun 2019 |
| 30305 | U. S. Energy Development Corporation | Fort Worth, TX 76164 | Oil & Gas Operator | Jul 2025 |
| 30306 | U. S. Operating, Inc. | Dallas, TX 75252 | Oil & Gas Operator | Jul 2025 |
| 30307 | U.S. Capital Corp Of Am, Inc. | | Oil & Gas Operator | Aug 1998 |
| 30308 | U.S. Enercorp, LLC | San Antonio, TX 78217 | Oil & Gas Operator | Jul 2004 |
| 30309 | U.S. Enercorp, LTD. | San Antonio, TX 78209 | Oil & Gas Operator | Sep 2019 |
| 30310 | U.S. Exploration Company | Houston, TX 77002 | Oil & Gas Operator | Aug 2003 |
| 30311 | U.S. Oil Reclaimers, LLC | | Oil Operator | Jun 2023 |
| 30312 | U.S. Sovereign Oil And Gas, Inc. | Dallas, TX 75355 | Oil & Gas Operator | Jul 2025 |
| 30313 | U.S. Steel Mining Co., Inc. | | Gas Operator | Jan 2000 |
| 30314 | U.S. Steel Mining Co., LLC | | Gas Operator | Oct 2002 |
| 30315 | U.S.A. Plugging Company | Pearsall, TX 78061 | Oil & Gas Operator | Jul 2025 |
| 30316 | U1 Ranch Oil | Houston, TX 77269 | Oil & Gas Operator | Jul 2025 |
| 30317 | Uae Investco 1 (Estill), LLC | Ravenna, KY 40472 | Oil Operator | Dec 2022 |
| 30318 | Uae Investco 2 (Lee), LLC | Ravenna, KY 40472 | Oil Operator | Dec 2021 |
| 30319 | Ubetco, Inc. | Rockdale, TX 76567 | Oil & Gas Operator | Jul 2025 |
| 30320 | Uebelhor, Theodore | | Oil Operator | Dec 2023 |
| 30321 | Uehlin LLC | Oberlin, KS 67749 | Oil Operator | Dec 2024 |
| 30322 | Uhc New Mexico Corporation | Midland, TX 79702 | Oil & Gas Operator | Feb 2007 |
| 30323 | Uhc Petroleum Corporation | Rocksprings, TX 78880 | Oil & Gas Operator | Jul 2025 |
| 30324 | Uhl Oil Co., Inc. | Bradford, PA 16701 | Oil & Gas Operator | Dec 2024 |
| 30325 | Uhls, Jimmie J. | Sedan, KS 67361 | Oil Operator | Sep 2019 |
| 30326 | Uinta Oil & Gas | Roosevelt, UT 84066 | Oil & Gas Operator | Nov 1997 |
| 30327 | Uinta Wax Operating, LLC | Fort Worth, TX 76107 | Oil & Gas Operator | May 2025 |
| 30328 | Uinta-Taylor Fund, LTD | Roosevelt, UT 84066 | Oil & Gas Operator | Nov 2018 |
| 30329 | Uintah Investors LLC | Vernal, UT 84078 | Oil & Gas Operator | May 2025 |
| 30330 | Ulatex Oil & Gas Inc. | Nocona, TX 76255 | Oil & Gas Operator | Dec 1998 |
| 30331 | Ullum Oil And Gas Development Corporation, Inc. | Grantsville, WV 26147-0000 | Oil & Gas Operator | Dec 2021 |
| 30332 | Ulrich, William J., Jr. & Connie K. | Elma, NY 14059 | Gas Operator | Dec 2024 |
| 30333 | Ultra Oil & Gas, Inc. | Centerton, AR 72719 | Oil & Gas Operator | Jul 2025 |
| 30334 | Ultra Petroleum (U.S.A.), Inc. | Granbury, TX 76048 | Oil & Gas Operator | Sep 2003 |
| 30335 | Ultra Production Company, LLC | Cedar Bluff, VA 24609 | Gas Operator | Oct 2014 |
| 30336 | Ultra Resources Inc | Houston, TX 77060 | Oil & Gas Operator | Sep 2018 |
| 30337 | Ultramar Oil & Gas LTD | Houston, TX 77060 | Oil & Gas Operator | Jul 1995 |
| 30338 | Ultramar Production Company | | Oil & Gas Operator | Dec 1991 |
| 30339 | Ulysses, City Of | Ulysses, KS 67880 | Gas Operator | Mar 2025 |
| 30340 | Umberham Oil Company Inc | Oklahoma City, OK 73151-4000 | Oil & Gas Operator | May 2025 |
| 30341 | Umc Petroleum Corporation | Houston, TX 77002 | Oil & Gas Operator | Mar 2015 |
| 30342 | Umma Resources, LLC | Portland, TX 78374 | Gas Operator | Jul 2025 |
| 30343 | Ummel'S Tank Ser | | Oil Operator | Sep 1994 |
| 30344 | Unbridled Resources, LLC | Houston, TX 77002 | Oil & Gas Operator | Jul 2025 |
| 30345 | Unc Texas Incorp | | Gas Operator | May 1987 |
| 30346 | Underground Energy Inc. | | Oil & Gas Operator | Apr 2025 |
| 30347 | Underwood Oil & Gas | Casper, WY 82602 | Oil & Gas Operator | Jun 2025 |
| 30348 | Underwood Oil And Gas LLC | Chandler, OK 74834-1414 | Oil & Gas Operator | May 2025 |
| 30349 | Underwood, Donald D. Dba Mustang Oil Co | Salem, WV 26426 | Oil & Gas Operator | Dec 2020 |
| 30350 | Underwood, Jim | Graham, TX 76450 | Oil & Gas Operator | Mar 2018 |
| 30351 | Underwood, Rip C | Amarillo, TX 79101 | Gas Operator | Sep 1963 |
| 30352 | Unger Well Drilling Corp | Dennison, OH 44621 | Oil & Gas Operator | Dec 1999 |
| 30353 | Uni Production Company, Inc. | | Oil & Gas Operator | Apr 1988 |
| 30354 | Unicon Producing Company | Houston, TX 75252 | Gas Operator | Mar 1994 |
| 30355 | Unicorn Drilling Inc | Cody, WY 82414 | Oil Operator | Dec 1998 |
| 30356 | Unicorn Energy, Inc. | Elgin, TX 78621 | Oil & Gas Operator | Jul 2025 |
| 30357 | Unicorn Oil & Gas Co Inc | Dorset, OH 44032 | Oil & Gas Operator | Dec 1993 |
| 30358 | Unifid Oil & Gas Corp. | | Oil & Gas Operator | Mar 1994 |
| 30359 | Unified Oil & Gas Corp. | Snyder, TX 79550 | Oil Operator | Jul 2025 |
| 30360 | Unioil | Denver, CO 80203 | Oil & Gas Operator | Jun 2012 |
| 30361 | Union Camp Corp | Dover, OH 44622 | Oil & Gas Operator | Dec 2002 |
| 30362 | Union City Boro Muni Auth Erie Cnty | Union City, PA 16438-1326 | Gas Operator | Dec 2024 |
| 30363 | Union Crude Company | Baytown, TX 77521 | Oil & Gas Operator | Apr 2018 |
| 30364 | Union Crude Operating Co. | Baytown, TX 77521 | Oil Operator | Aug 2003 |
| 30365 | Union Development Company Inc | | Oil & Gas Operator | Dec 1992 |
| 30366 | Union Diversified, Inc. | | Gas Operator | Dec 2008 |
| 30367 | Union Drilling &Management Inc | | Gas Operator | Feb 1991 |
| 30368 | Union Exploration Partners, LTD. | | Oil & Gas Operator | Aug 1990 |
| 30369 | Union Gas Operating Company | Houston, TX 77014 | Oil & Gas Operator | Jul 2025 |
| 30370 | Union Oil Co | Danville, OH 43014 | Oil & Gas Operator | Dec 2014 |
| 30371 | Union Oil Co Of California | Midland, TX 79706 | Oil & Gas Operator | Jan 2022 |
| 30372 | Union Operating Corp | Lakewoord, CO 80215 | Oil Operator | Dec 2023 |
| 30373 | Union Pacific Austin Chalk Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Jan 2001 |
| 30374 | Union Pacific Re | | Oil & Gas Operator | Dec 1996 |
| 30375 | Union Pacific Resour | | Oil & Gas Operator | Apr 2002 |
| 30376 | Union Pacific Resources Co. | Fort Worth, TX 76101 | Oil & Gas Operator | Sep 2002 |
| 30377 | Union Petro Inc | Uniontown, KY 42461 | Oil Operator | Dec 2023 |
| 30378 | Union Petrochemical | | Oil & Gas Operator | Dec 1982 |
| 30379 | Union Producing Co. | | Gas Operator | Dec 1992 |
| 30380 | Union Royalty, Inc. | Midland, TX 79706 | Oil & Gas Operator | Jul 2014 |
| 30381 | Union Seaboard Corporation | Houston, TX 77024 | Oil & Gas Operator | Mar 2008 |
| 30382 | Union Springs Central School District | Union Springs, NY 13160 | Gas Operator | Dec 2024 |
| 30383 | Union Texas Petroleum | Houston, TX 77252 | Oil & Gas Operator | Oct 1991 |
| 30384 | Union Texas Petroleum Corp. | Houston, TX 77252-2120 | Oil & Gas Operator | Dec 2014 |
| 30385 | Union Valley Petroleum Corporation | Enid, OK 73701 | Oil & Gas Operator | May 2025 |
| 30386 | Unionville Explo | | Oil Operator | Jul 1984 |
| 30387 | Unit Drilling & Exploration Co | Tulsa, OK 74132-5300 | Oil & Gas Operator | Apr 2025 |
| 30388 | Unit Manager, Citronelle Unit | | Oil & Gas Operator | Sep 2001 |
| 30389 | Unit Petroleum Company | Tulsa, OK 74170 | Oil & Gas Operator | Jul 2025 |
| 30390 | United Company | Lubbock, TX 79408 | Oil & Gas Operator | Jun 1995 |
| 30391 | United Energy & Expl Inc | Ada, OK 74821-2449 | Oil & Gas Operator | Apr 2025 |
| 30392 | United Energy & Exploration LLC | Ada, OK 74821 | Oil & Gas Operator | Apr 2025 |
| 30393 | United Energy Corporation | San Antonio, TX 78209 | Oil & Gas Operator | Jul 2025 |
| 30394 | United Energy Develop Co LTD | Bartlesville, OK 74003 | Oil Operator | Mar 2004 |
| 30395 | United Energy Inc. | Wichita, KS 67230 | Oil & Gas Operator | Dec 2002 |
| 30396 | United Energy Operating, LLC | Edmond, OK 73083 | Oil & Gas Operator | Jul 2025 |
| 30397 | United Energy Partners, Inc. | Dallas, TX 75201 | Oil & Gas Operator | Mar 2008 |
| 30398 | United Fuel Gas Co | | Oil & Gas Operator | Dec 2022 |
| 30399 | United Gas Pipe Line Co. | | Oil Operator | Aug 1993 |
| 30400 | United Investment Group | | Oil Operator | Nov 2004 |