Compared to wood fuels, coal yields a higher amount of energy per mass and can often be obtained in areas where wood is not readily available. Though it was used historically as a domestic fuel, coal is now used mostly in industry, especially in smelting and alloy production, as well as electricity generation. Large-scale coal mining developed during the Industrial Revolution, and coal provided the main source of primary energy for industry and transportation in industrial areas from the 18th century to the 1950s. Coal remains an important energy source. Coal is also mined today on a large scale by open pit methods wherever the coal strata strike the surface or are relatively shallow. Britain developed the main techniques of underground coal mining from the late 18th century onward, with further progress being driven by 19th century and early 20th-century progress. However, oil and gas were increasingly used as alternatives from the 1860s onward.