Formation pressure is gas pressure in gas-saturated volume of a formation. There are initial and current formation pressures. Initial formation pressure takes place in the gas-saturated volume of the formation before the start of development. Initial formation pressures are usually extrapolated to an average horizontal plane passing through the gravity center of the gas-saturated volume and, more often, through the center of a productive stratum.

Current formation pressures are formed in the gas-saturated volume during gas extraction from it by a system of operational wells. Its distribution in the gas-saturated volume is characterized by isobar maps and pressure sinks.