Quirks & Quarks

Quirks Question: How much oil have we taken out of the ground?

And what's taken the oil's place under the ground?
Pumpjacks pump crude oil near Halkirk, Alta., June 20, 2007. (Larry MacDougal/Canadian Press)

How much oil have we removed from the ground, and what's taken its place?  According to Astrid Arts, a staff geologist with Cenovus Energy in Calgary, we've probably removed about a trillion barrels of oil from the Earth since we started extracting it commercially in the 19th century.  That's about six million Olympic-sized swimming pools.  But that doesn't leave large voids underground - oil is usually found in "spongy" rock or porous sand deposits. When oil is removed it leaves small gaps which are filled with water or gas.  There is a pressure reduction in the area from which oil or gas has been removed, and on rare occasions this has led to land subsidence or even small earthquakes.