What about heavy oil, oil shale, tar sands?
Wyoming, Utaah, Colorado, Alberta, Venezuela?
etc.
They are there for the taking at some future time.
The reason Oil sands in Wyoming, etc got onto the radar as they are extremely large deposits. The reason they have not been commercialized much is the costs are exhorbitant. Basically, one must mine them like coal to process the hydrocarbons out of the rock - expensive and environmentally challenging. Some people like Shell have tested microwaving technology to retort in situ but economics never cut it.
Heavy oil and tar sands far and away are the most successful tertiary recovery mechanism ever found. In this country, lots of oil production by steamflooding continues in California that is very competitive with conventional oil production economics. The basins in Athabasca(Alberta) and Orinoco(Venezuela) are the largest on earth in terms of potential yield of heavy oil/tar sand volumes but the API gravity is so low fluid does not flow easily, at times even with steamflood assist. So economics are suspect.
The paradigm shift in my mind is the abundance in this country of natural gas via unconventional methods. It is first an environmental-friendlier alternative than the oil shales, heavy oil or tars. Secondly, there is so much of it that prices are in stagnation mode, making it commercial to even liquify it and export to other countries as we do presently.
The nature of natural gas is that its hydrocarbons can be rearranged to produce synthetic liquids, whether it is gasoline, kerosene or diesel, using proven technologies. The key is the price of raw feed, which is attractive right now.
One of the beauties of creating synthetic liquids is the end product contains no contaminants whatsoever, it is 100% pure - so no by product pollution in the air or in your engine to mess with. A very agreeable liquid to burn.