Ethanol, methanol, biodiesel, LPG, whatever.
"Scarce oil" is a very popular theme to get people concerned over, though. Been coming up for as long as I can remember. The emotional & political appeal is very great, if you can manage to convince people to ignore how plentiful and cheap oil has proven to be.
We'll be just fine with or without oil. We survived 8 million years before it was "discovered", and we have energy production and conservation technologies now that were completely unimaginable just 60 years ago.
Hell, if the world could survive on whale blubber for hundreds of years, then maybe liposuction will be our energy future!