Oil shale is a form of sedimentary rock which contains compounds which can be converted into hydrocarbons. In fact, the term “oil shale” is a bit of a misnomer, since oil shale isn't actually shale, and it doesn't contain oil, either. Worldwide deposits of oil shale could potentially yield around three trillion barrels of oil, if processed efficiently, and many oil companies aim to improve the efficiency of their extraction process to make this number even higher. As such, oil shale is viewed as a potential alternative to crude oil extraction, in response to concerns about dwindling crude oil reserves.
Like crude oil, oil shale contains a large amount of organic material. In oil shale, this organic material forms compounds known as kerogens, which can be extracted from the rock by heating it to create a vapor. The vapor can then be distilled to create various hydrocarbon chains, ranging from heating oil to gases. Oil shale has also historically been used as a source of fuel, because the rocks will literally burn, thanks to their kerogens.
Processing oil shale is not without serious environmental repercussions. First, the rock must be extracted, generating a variety of issues associated with mining including erosion and pollution. Then, the rock has to be treated to extract the kerogens. During the treatment process, the rock expands, making it difficult to put back into the mine once the area has been stripped, and the rock is also carcinogenic, so it is difficult to dispose of safely. The distillation process also eats up a lot of resources, making it even less efficient than traditional crude oil distillation.
Oil shale processing programs have been piloted in several countries; the rock itself has been used in industrial processes since the 1800s. However, large scale mining and processing of oil shale has met with serious opposition from many environmental organizations, with members fearing that it could degrade the environment while encouraging a reliance on fossil fuels. The thought of digging up vast swathes of the natural landscape for the purpose of extracting fuel is also extremely distasteful to many activists, who are concerned about the Earth's remaining wilderness areas.
In the early 21st century, when oil prices began to rise quite dramatically, many people looked to shale oil, oil-bearing sands, and bituminous rock as potential sources of energy. However, these sources are ultimately only a temporary stopgap, as eventually reserves of these materials will disappear as well, leaving people facing a serious energy crisis. In the short term, conversion to such materials could drive energy prices up even higher, as a result of the labor required to render them usable.