Gas was created at the same time as oil. When the sediment piled up and solidified, part of the organic waste turned into oil or gas, in the tiny spaces between the grains of sediment.

The layers containing gas and oil were encased in impassable layers of stone. Then, as the oil was heavier, it moved to the bottom, and the gas to the top. That is why gas is found before oil at drillings.

Once, gas's usefulness was not realised. It was allowed to escape or burned. But today, and increasingly since the oil crisis, natural gas has taken on great importance in industrial countries. Almost everywhere oil is found, natural gas is also found.
A large discovery of natural gas was made in Lacq in France in 1951. Deposits measured 200 million cubic metres (2615 million cubic yards). Raw gas is extracted from about 30 rigs. The pure gas is sent across France through a network of pipelines. Fuel, butane, propane and sulphur are recovered from the gas purification (sulphur production covers all France's needs). Gas sustains many industries.