What is Gas Formation Volume Factor (FVF)?

Gas formation volume factor (FVF) is a measure of the natural gas volume contained in a reservoir under specific temperature and pressure conditions, relative to the volumes would be present under standard temperature and pressure (STP) conditions. The FVF is used to calculate gas reserves and production rates. FVF is defined as the ratio of the gas volume at reservoir conditions (measured in cubic feet or cubic meters) to the gas volume of gas at STP conditions (measured in standard cubic feet or standard cubic meters).