The Gas for our cars is the least of our problems, but the one that everyone always focuses on.
"Renewable" or "Alternative" fuel sources can't be used to make our foods, our plastics, our chemicals, or the millions of other things produced with Oil. And many "alternative" fuel sources require significant amounts of energy to create and use.
Quite simply there is nothing that can replace Oil. We'll be able to drive our cars with other products -- too bad we won't be able to build them without huge amounts of oil.
And don't even get me started on a Public Transportation rant.
