The non-conventional oil

Some deposits are formed by oil denser, more viscous, such as oil shale, the extra-heavy crude, or tar sands. Their use is often difficult: there must be thin the oil before being able to extract it. Processes to make these types of oil used are numerous and very energy efficient. While some of these deposits are already exploited, the vast majority is unlikely to be that when the price of oil will be high enough to justify it. The reserves of unconventional oil usable (15% of total) are estimated at 600 billion barrels, equivalent to half of the proven resources.