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The economic life of the human race had for some time been based on coal, but latterly oil had been found a far more convenient source of power; and as the oil store of the planet was much smaller than its coal store, and the expenditure of oil had of course been wholly uncontrolled and wasteful, a shortage was already being felt. Thus the national ownership of the remaining oil fields had become a main factor in politics and a fertile source of wars.
— OLAF STAPLEDON