It has been estimated that 2.8 to 3.3 trillion barrels of oil shale exist in the world, with the United States carrying 1.5 to 2.6 trillion of these (1). This is more than all the conventional oil reserves that existed in the world. We would not run out of these reserves in the near future. Oil sands from only Canada and Venezuela total 3.6 trillion barrels (2), which helps us avoid the problem of scarcity. However, there are countless limitations and environmental impacts.
The above diagram shows the ranges of EROI (which is the same measurement as EROEI) for oil sands from various studies. They tend to stay low from 1.5 to 4, with some rarer areas where it can go as high as 7 to 13 (3) (4). EROI for oil shale tends to be roughly the same or lower.
The main difference between oil shale and oil sands is that the latter is easier to harvest due to the water content it contains between the sands and the oil (5). In the Athabasca Oil Sands of Alberta, Canada, only 475 million barrels of oil from the oil sands are extracted annually. The producers (note that they would be biased towards optimistic projections) foresee an increase of this to 1.1 billion barrels of oil annually by 2018 (6). This is still a far cry from 2008's global demand of 31.1 billion barrels of oil annually.
The above shows what used to be a borreal forest and is now an open pit mine for oil sands.
Mining oil shale and oil sands causes a significant amount of environmental damage. A Pembina Institute report stated that "to produce one cubic metre (m3) of synthetic crude oil (SCO) (upgraded bitumen) in a mining operation requires about 2–4.5 m3 of water (net figures). Approved oil sands mining operations are currently licensed to divert 359 million m3 from the Athabasca River, or more than twice the volume of water required to meet the annual municipal needs of the City of Calgary" (7). Nutrient runoff and eutrophication are significant concerns. The "toxic tailing lakes", or the dump areas for the polluted water that comes out of the fresh water input in oil sand mines, are up to 50 kilometers long and are highly visible in space:
The mining and processing of 1000 million tons of oil shale in Estonia has created about 360-370 million tons of solid waste, of which 90 million tons is a mining waste, 70–80 million tons is a semi-coke, and 200 million tons are combustion ashes (8). The carbon footprint is higher than that of conventional oil with up to 4 to 6 times more emissions (9) (10). Oil sand extraction technology is more developed than that of oil shale, which explains why the United States has been importing Canadian oil sand resources instead of producing oil shale. Most oil shale is harvested through strip mines, which produce tremendous waste known as spent oil shale. Around 1.5 tons of spent oil shale is produced for every one barrel of converted oil (10). However, many companies are patenting their ideas of in situ mining, which is basically converting the oil shale to usable oil on the spot instead of shipping it elsewhere for processing. They basically install electric heaters in the ground and heat the oil shale for about 3 years to convert it into crude oil. Although this sounds ineffective, they predict an EROEI of at least 3 (10).