In the second half of the 20th century, oil shale

In the second half of the 20th century, oil shale production ceased in Canada, Scotland, Sweden, France, Australia, Romania, and South Africa due to the low price of oil and other competitive fuels.[15] In the United States, during the 1973 oil crisis businesses expected oil prices to stay as high as US$70 a barrel, and invested considerable sums in the oil shale industry. World production of oil shale reached a peak of 46 million tonnes in 1980.[15] Due to competition from cheap conventional petroleum in the 1980s, several investments became economically unfeasible.[15][16] On 2 May 1982, known as "Black Sunday", Exxon canceled its US$5 billion Colony Shale Oil Project near Parachute, Colorado because of low oil-prices and increased expenses.[17] Because of the losses in 1980s, companies were reluctant to make new invests in shale oil production. However, in the early 21st century, USA, Canada and Jordan were planning or had started shale oil production test projects, and Australia was considering restarting oil shale production.[15][18]

In a 1972 publication by the journal Pétrole Informations (ISSN 0755-561X), shale oil production was unfavorably compared to the liquefaction of coal. The article stated that coal liquefaction was less expensive, generated more oil, and created fewer environmental impacts than oil shale extraction. It cited a conversion ration of 650 litres (170 U.S. gal; 140 imp gal) of oil per one ton of coal, as against 150 litres (40 U.S. gal) per one ton of shale oil.[19]
Energy usage