Hubbert's graph of peak oil

Hubbert's prediction for the United States (red) and actual production (greeen)

Peak oil is the idea that at some point an oil well, an oil field, a country, or the world, will be producing the most crude oil it can ever produce at one time. After this point, less oil will be produced and therefore people will have to use less oil because it will cost more money. Many scientists and governments are concerned about what will happen when there is less oil to go around.