oil
a barrel of oil has lots of energy in it. how much exactly is an interesting question that can be answered pretty easily. just convert it to man hours of labor. take a moment to take a guess how many man hours of labor are in a barrel of oil. close your eyes and think about your answer for a minute. go ahead. no one's looking. the answer is surprisingly large. staggering even. in a single barrel of oil there are fifteen man /years/ of labor. we pay $60 per barrel. at that rate my salary should be $4 a year.