The bay has Britain's second-largest natural gas field, in the Triassic Sherwood Sandstone with a seal of Mercia Mudstone and a Carboniferous source. The South Morecambe Field, covering an area of , was discovered in 1974 and the first gas came ashore in 1985. The North Morecambe Field, found in 1976, to the north, is and started production in 1994. Both are operated by Centrica Energy. They are west of Blackpool in 30 metres of water; the top of the gas reservoir is at a depth of just , necessitating slant drilling for the first time in European waters. The combined gas reserves on discovery were estimated at 179 billion cubic metres (6.45 trillion cubic feet (tcf)). A further 0.65tcf is recognised in the satellite fields of Bains, Calder (Rivers), Dalton, Millom East and Millom West, and a number of smaller fields have been identified.