That is true - but I believe that extraction and refining is a much bigger contributor to oil's footprint, compared to coal's. It is also far more variable.
To turn a barrel of tar sands oil into gasoline, for example, adds another ~230 pounds of CO2 to the atmosphere - in addition to the emissions from burning it. That's ~40 pounds/million BTU.
It almost costs us more energy to mine and refine tar sands oil, then we get out of burning it.
