The Alberta oil sands in Canada are thought to contain approximately one third of the world's oil resources; it is estimated that some 300 billion barrels of oil from the sands are ultimately recoverable, equal to or greater than the reserves of Saudi Arabia.
But just because reserves of unconventional oil are large, it does not mean they will ever be produced in quantities like conventional oil. Much of the oil-sand is too deep to be reached by strip mining. Other methods are being tried to recover this deeper oil, but the economics are marginal. With the strip mining and refining process now in use, it takes the energy equivalent of two barrels of oil to produce one barrel. To expand the strip mining operation to the extent which could, for example, produce the 18 million barrels of oil used each day in the United States would involve the world's biggest mining operation, on a scale which is simply not possible in the foreseeable future, if ever.