Several years ago the USGS predicted that the Monterrey Shale in California would have 15 billion barrels to extract.  Then they said 600 million.  Now they say 26 million.

The heavy crude is a euphemism for tar sands, which are not actually petroleum.  It takes a huge input of energy to cook this stuff so it can be used as a fuel.  It's barely an energy "source."

Colin Campbell, the petroleum geologist who coined the term Peak Oil, said that in the reports about how much oil is extractable the only accurate figures are the page numbers.  The trick is to figure out which claims are closer to reality than others.  There is also a huge difference between easy to extract oil that can be drilled and gooey tar sands that take almost as much energy to cook as they contain.  Tar sands are like a desperate cigarette smoker looking through an ash tray to find a butt that might have a puff or two if relit.  No one would frack or mine tar sands if the easy, quality oil was still abundant.