"...developing new sources like oil shales and tar sands."
I'm going from memory here...oil shale becomes economically feasible at ~$50.00 bbl for crude. Why else would the Saudis open the spigot like they have? Oil shale technology isn't complete, but it will become so if oil stays over $50.00.
Do a search on Shell. There is a thread where they have found a way to make it feasable at $30 per barrel. And at that price there were comments that there is the equivalent of 1.7 TRILLION barrels in the Colorado Green river valley alone.
Recently an article detailed a Shell project that is feasible at less than $30 a barrel, and totally effective.