Underutilization of heavy oils as an energy source

Heavy oils can be pumped just like conventional petroleum except that they are much thicker, more polluting, and require more extensive refining.
Heavy oils are found in more than 30 countries, but about 90% of estimated reserves are in the Orinoco "heavy oil belt" of Venezuela, which has an estimated 1.2 trillion barrels. About one third of the oil is potentially recoverable using current technology.
(E) Emanations of other problems