Since much artificial fertilizer is produced from the side and waste products of the oil industry, this is the point where the food problem touches on the problems of the availability and the price of oil. Any serious rise in the price of oil also increases the price of artificial fertilizer or of the by-products of the oil industry from which it is being made. Thus, any serious increase in the price of oil threatens indirectly but fairly immediately the food supply of Third World countries that are always hard pressed for the cash to pay for those imports. The main consequence of a price rise in oil is, of course, a rise in the price of gasoline, which drives not only cars but whole industries in both industrialized and developing countries-including water pumps and the machinery for large-scale irrigation of fields. In the 1920s, total oil reserves were estimated at 8,000 million tons.