1. n. [Geology]

A bounding surface in a reservoir above which predominantly oil occurs and below which predominantly water occurs. Although oil and water are immiscible, the contact between oil and water is commonly a transition zone and there is usually irreducible water adsorbed by the grains in the rock and immovable oil that cannot be produced. The oil-water contact is not always a flat horizontal surface, but instead might be tilted or irregular.

Alternate Form: OWC

See: downdip,  fluid contact,  gas-oil contact,  gas-water contact,  immiscible,  miscible,  reservoir,  updip