Depositional environments determine the basic architecture and geometry of siliciclastic hydrocarbon reservoir rocks. In nonmarine settings, sandstone reservoirs are deposited in fluvial, eolian, and lacustrine environments, whereas in marine settings these reservoir rocks are in deltaic, shallow marine, and deep marine settings. Facies and reservoir rock properties of giant oil and gas fields in each depositional setting are tabulated and described. The most prolific sandstone reservoirs are deposited in marine deltaic distributary mouth bars and distributary channels in delta lobes. Stacking of delta lobes by channel avulsion and subsidence of inactive lobes due to compaction of the underlying prodelta silts and clays greatly increases the volume of reservoir sand. Tert ary deltaic sediments, underlying major modern deltas, offer likely places to find these reservoir rocks in rollover anticlines. Shallow marine sediments provide the next most prolific reservoir facies, which are deposited as barrier islands, beach, shoreface, and offshore bar sands. Great potential exists for siliciclastic reservoir rocks in deep marine fans, a relatively underexplored target occurring at the base of delta slopes or in rift or wrench basins. Advanced three-dimensional seismic technology and the present knowledge of seismic and sequence stratigraphy should help locate these sandstone reservoirs. Nonmarine reservoirs offer excellent targets in some basins, such as the fluvial sands of North Africa and the underexplored lacustrine-related reservoir rocks of China. Because f their high quality, areal extent, and thickness, eolian sand reservoirs must always be considered, particularly in continental interior strata with paleolatitudes in the 15°-40° range north and south of the paleoequator.