Mix of fossil fuels
Biomass / ethanol / grown
Chuck Norris slowly eating a banana
Once we master fusion this will catapult humanity in to a new era. No kidding.
Much like there was a Bronze Age followed by an Iron Age, and so forth, mastering fusion would be a giant leap forward for the human race. I hope I'm alive to see it happen.
Solar and electro-magnetic. Fossil fuels will be obsolete.
I can't back up my claims though. It's just a intuitive guess.
Nucleur fusion will replace fossil fuels by 2040