Since 1950, the share of world energy production provided by fossil fuels has varied only slightly between 85 and 93 per cent. (rstb.royalsocietypublishing.org)
The share of petroleum liquids in world energy production grew rapidly during the 1950s and 1960s, reaching half of all energy production in 1973. (rstb.royalsocietypublishing.org)
From 1950 to 1985, the share of natural gas in world energy production doubled, rising from just over 10 per cent to just over 20 per cent. (rstb.royalsocietypublishing.org)