I wrote to Glenn Morton about the numbers from John Hunt -- he who estimated that there is 50 times more carbon in coal than in the present biosphere. Here is what he said:

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I think the thing you are missing is that Hunt calculates disseminated carbon in the form of carbonaceous material and disseminated petroleum. The quantities of economically recoverable oil are tiny in relation to the quantities that can't be recovered. Only 30% of the oil in most oil fields can be actually pumped out of the ground. And the oil in oil fields is a tiny tiny fraction of all the petroleum found in rocks, most of it too dispersed to be of any value at all.


The link I gave with the table that said 4 trillion tons was labeled "fossil fuel deposits." Those would be the quantities of recoverable coal and oil that could be used for fuel -- a number that would be important to people for obvious reasons, hence the numerous similar estimates for this. The rest of the carbon in the rocks, unusable, would not be of so much interest. As I suspected, it's a matter of knowing exactly what the numbers are referring to. Glenn and Hunt are both petroleum geologists so they have expertise in this area.

Note that I'm willing to admit when there's an apparent discrepancy in my sources, and that I check it out. Denial is unscientific.