When the epoch of liquid fuels began with the opening of the first oil well in about 1860, the conditions were created for the enormous technical development which motorization brought about within industry, commerce, agriculture, and transportation. Although the world's oil reserves have been adequate so far, the continuing rapid advance in the use of motor vehicles has created an oil demand which the petroleum industry has not always been able to satisfy. This is largely due to the uneven distribution of these reserves over the face of the earth. The struggle of the nations for their vital needs has often been centered around oil. Great resources have been mobilized in order to develop new liquid fuels comparable or superior to petroleum, and the recovery of oil from oil shale figures prominently among the possibilities of utilizing other available sources of supply. Oil shale deposits of varying sizes occur in most countries, bearing potential oil reserves estimated to total about 175 billion tons.