"Hard to see why someone would refer to shale oil/gas or even tar sands as "unconventional energy sources"..."
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Ben, I'm sure the late Matt Simmons used to refer to shale oil/gas/tar sands as non-conventional energy sources versus more traditional sources of natural gas and oil.
Conventional vs non-conventional, cheap vs non-cheap.
Ok, tech advances might be bridging the cost gap.... a little
