1. n. [Geology]

A bounding surface in a reservoir above which predominantly gas occurs and below which predominantly water occurs. Gas and water are somewhat miscible, so the contact between gas and water is not necessarily sharp and there is typically a transition zone between 100% gas and 100% water in reservoirs.

Alternate Form: GWC

See: fluid contact,  gas-oil contact,  immiscible,  oil-water contact,  reservoir