Ubbehohde viscosimeter
A suspended level apparatus for accurately determining the viscosity of a liquid
Ullage
The amount which a tank or vessel lacks of being full
Underground blowout
an uncontrolled flow of gas, salt water, or other fluids out of the wellbore and into another formation
Underground storage
The storage of natural gas in underground reservoirs at a different location from which it was produced.
Unitization
the joint development of a petroleum resource that straddles territory controlled by different companies