(This post is by Ianqui from The Oil Drum).
That oil is consumed by public and private transportation and industry is a no brainer.
However, another, perhaps more important reason petroleum is so vital to our economy, beyond transportation, is that it takes a lot of fossil fuel just to produce the food that we eat every day.
When I stop to think about this, I get this image of gasoline being poured on my food. Pictured that way, the idea that we use a lot of oil on food is easy to dismiss, but the truth is that there are myriad ways that oil makes it into the food chain. And this is something we must be aware of, since once there are oil shortages, it's not just going to be lines at the pump--there might also be lines at the grocery stores.