The USGS defines oil field as: "Area where petroleum is or was removed from the Earth.
Because the oil reservoirs typically extend over a large area, possibly several hundred kilometres across, full exploitation entails multiple wells scattered across the area.
In addition, there may be exploratory wells probing the edges, pipelines to transport the oil elsewhere, and support facilities.
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.