Let's say the energy cost of building a new bridge is $500,000 worth of hydrocarbons. Now, let's compare that to non-hydrocarbon energy sources. Historically, this might be steam from burning wood, or a team of mules. What I am saying is that $500,000 worth of wood or mules is so much less energy than $500,000 worth of oil, that the oil is nearly free in comparison.

Think about it: what other fuel is just sitting around, storing millions of years of solar energy, and waiting to be extracted and burned???

This is a key economic concept that must be understood when discussing oil.