1. . 
A subsurface body of rock having sufficient porosity and permeability to store and transmit fluids. Sedimentary rocks are the most common reservoir rocks because they have more porosity than most igneous and metamorphic rocks and form under temperature conditions at which hydrocarbons can be preserved. A reservoir is a critical component of a complete petroleum system.
See: aquifer, basement, caprock, condensate, dolomitization, downdip, fairway, fluid contact, formation pressure, gas-oil contact, gas-water contact, hydrocarbon, impermeable, in situ, oil-water contact, pay, pinch-out, play, primary migration, prospect, seal, secondary migration, sequence stratigraphy, spill point, time-lapse seismic data