Peak Oil Production
In the US oil production grew steadily until 1970 and declined thereafter, regardless of market price or improved technologies.
In 1956 M. King Hubbert, a geologist for Shell Oil, predicted that the peaking of US Oil production would occur in the late 1960's. Although derided by most in the industry he was correct. He was the first to assert that oil discovery, and therefore production, would follow a bell shaped curve over its life.
After his success in forecasting the US peak, this analysis became known as Hubbert's Peak. World discovery of oil peaked in the 1960s, and has declined since then. If the 40 year cycle seen in the US holds true for world oil production, that puts global peak oil production, right about now; after which oil becomes less available, and more expensive.