- Unbiased Geotherma = TGN
- Unbiased Geothermal Temperature Gradient = GradTGN
- Unbiased Geothermal Temperature Profile = TGN
- Unbiased Geothermal Temperature Profile = UTG
- Unconventional Reserves
- Undersaturated oil
- Undersaturated Oil Reservoir
- Unit (measurement)
- Unit-rate
- Unit-rate transient response = UTR
- Unit-rate Transient Response Spider-plot = UTRS
- Units Systems
- Universe
- Unrecoverable reserves
- Unstructured grid (irregular grid)
- Unweighted Productivity Plot = Unweighted J-plot
- Upscaling
- Upstream (Exploration & Production = E&P)
- Utrasonic defectoscopy