Energy Usage at a Macro Scale  One thing we can be sure of when
it comes to energy - we use a lot of it. According to the US
Energy Information Administration (EIA) the US used 97.5
quadrillion btus of primary energy in 2011.  That is
97,500,000,000,000,000.  So where did all of this energy come
from?  The largest primary energy source is petroleum which
accounted for 36 percent of energy use in 2011. This is followed
by natural gas at 25 percent, coal with 20 percent, renewables
at 9 percent, and nuclear at 8 percent.  In future posts we will
devote a bit more time to each primary energy source and
consider how this usage has changed over time.