The catastrophic crash of an oil-carrying train in the province of Quebec last month, which devastated the town of Lac-Mégantic and killed dozens, has brought the Keystone XL pipeline into the headlines again. For many environmentalists, the train crash is just one more reminder of the risks of fossil fuel production – that the train was carrying tar sands oil was, as it were, the icing on the cake. Conversely, for many supporters of the pipeline, the train crash proves that we need Keystone. But first a word on tar sands and the other unconventional oil sources now being extracted such as shale oil. Unlike conventional oil wells, shale and tar sands do not contain liquid oil. Oil must be extracted from them in a process that is quite similar to mining. The development of Canadian tar sands requires vast deforestation in order to dig up and process the sands, and shale oil extraction requires that massive amounts of rocks be mined and processed.