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Tar Sands or Oil Shales are a natural formation which oil has been absorbed into the materials in the ground rather than trapped in pockets, making them generally difficult to extract using traditional techniques. The potential amount of available oil in this form is actually greater than that pumped out of the ground so far in all of history. There was an extensive government program in the 70s to develop recovery techniques but the technology wasn't there, and the subsequent collapse of the price of oil in the 80s caused research funding to be substantially decreased. With the passage of time, however, new technologies have made the extraction of oil from these reserves much more practical at a lower fixed, inflation-adjusted price-per-barrel than they have been at any point in history. While the current as-I write price of oil per barrel has fluctuated too low to justify development, it is expected that the price will likely go above that point to stay within not long after the length of time it takes to develop such resources. Interestingly enough, some of the largest known oil deposits in the world in this form lie in the USA and Canada. The current major problems regarding the development of these resources are currently legislative and bureaucratic, more so than technical.