Billion cubic meters of natural gas (bcm) is a unit of energy, specifically natural gas production and distribution. There are different standards for how much energy this represents, but according the International Energy Agency (IEA) it is equal to 38.2 petajoules (1.06 x 1010 kWh) at 15°C and atmospheric pressure. This is an extremely large amount of energy. In 2013 the global natural gas demand was estimated at 3 500 billion cubic metres.
Oddly 1 BCM = 1 cubic km.