English: Continuous hydrocarbon reservoirs, identified by play numbers of the 1995 USGS National Assessment.[1]

Continuous hydrocarbon accumulations are mineral fuel deposits not limited by water blockage. Most material is natural gas.

The USGS now includes unconventional oil and gas resources in its National Assessment of Oil and Gas Resources and investigates complex properties of continuous hydrocarbon reservoirs. Standard methods for quantitative resource assessment are inappropriate because continuous-type accumulations are large single fields having areal dimensions of miles and are not significantly affected by hydrodynamic influences. USGS geologists not only quantify the amount of technically recoverable resource, but more importantly, they estimate the amount of resource that might become available for human activity over a reasonable period of time. For example, as much as 5,000 trillion cubic feet of gas is locked up in continuous accumulations of the Green River Basin alone, yet only a fraction of it will ever be recovered. By comparison, the total proved reserves of gas in the entire United States are approximately 160 trillion cubic feet.