Reply First the tens of thousand more heavy oil than lightr crude is false To get this figure you probably included all organic content in the lithosphere as if there was a remote chance to gzet anything usable from a 5 km deep shale with 1 of kerogen You got confused light oil and conventionnal oil what you categorized as low grade oil is for a large part not oil at all kerogen Second there is a important notion you ignored net energy yeld The vast majority of low grade fossil fuels like deep oil shale would consume more energy to extract than they would give Already the Athabasca oil sands have a self consumption of about 30 that could be reduced to some 25 with advanced technology The small sclae oil shale projects that were teste had a near zero net energy yields except in estonia but the shales they used were among the richest known Third extraction rate is as important as reserves Non conventionnal oil biodegraded oil bitumen oil heavier than water is very difficult to take out Kerogen from shale is even worst Even if these ressources are in the trillions of barrels they won t provide much help if we can only get a few million barrels out per day Fourth non conventionnal has an high environmental cost CO2 emeissions on a full cycle basis from well to end use are much higher There are other problems like the destruction of ecosystems for open pit production of both oil shale of oil sands water use especially for oil shale water pollution disposal of wastes for oil shales These environmental costs would become catastrophic is non conventional production was to be upscaled to the same range of output than current conventional production