You don't have to dig up fossil fuels, we can grow it if it comes down to that.
World-First Biofuel Test Flight - Cheap Flights, Airfares & Holidays - Air New Zealand Official Site - NZ
Early days so it's not practical yet on many levels - but expect the wonders of science to increase yields from such crops in order to both reduce the land required to grow it, and reduce the price "at the pump".