Short Definition
An underground formation where oil or gas accumulates.
Extended Definition
A reservoir is a subsurface rock formation with enough porosity and permeability to store and transmit hydrocarbons. It sits beneath a sealing layer, allowing oil or gas to collect in place until produced by wells.
What It Means to an Investor
Reservoir quality and size drive recoverable volumes and production rates, shaping reserves, cash flow, and valuation.
