This is a very tough issue to deal with because the variables are so extensive. There are estimated to be well over 2 trillion barrels in oil sands and oil shale. This is something like 10 times the total Saudi Arabian proven reserves.

However, there are a couple of catches. No one really knows how much of that is recoverable at any cost. Much of those reserves are in Arab countries and Venezuela so it doesn't change the geopolitical situation all that much. However, the North American reserves probably exceed the current Saudi proven reserves.

Recovery requires a significant amount of heat. If that is produced by burning oil, the CO2 impact is much higher than conventional oil. That is why the Canadians are looking at nuclear plants to provide the heat. However, current plans still require a lot of water and there are issues with water availability and discharge quality.