URL: 

oil field

1. n. [Geology]
An accumulation, pool or group of pools of oil in the subsurface. An oil field consists of a reservoir in a shape that will trap hydrocarbons and that is covered by an impermeable or sealing rock. Typically, industry professionals use the term with an implied assumption of economic size.
2. n. [Geology]
The surface area above a subsurface oil accumulation is called an oil field.