Americans use more energy per person than any other country, though they make up only 6% of the world's population. In 1975, the total US energy costs were around $170 billion, and energy needs have risen each year since. Most US energy comes from crude oil, and since domestic production cannot meet demand, nearly half of oil used is imported. Estimates suggest the US has a 25-30 year supply of domestic oil remaining, which could be depleted by 2007 if consumption continues as-is, and natural gas supplies may run out even sooner. As energy demands and prices continue increasing, the availability and cost of future supplies remains uncertain.