Recent estimates of world recoverable oil resources are consistent with an estimate of oil in place in conventional remaining oil reservoirs on the order of 4,900 billion barrels, exclusive of extra-heavy oil and natural bitumen. On a comparable basis, the remaining oil in place in Venezuela’s Orinoco Oil Belt, comprised of extra-heavy oil, is about 2,000 billion barrels, plus 235 billion barrels of contingent (lesser known) resources. Similarly, in northern Alberta, Canada, there is an additional 1,455 billion barrels of natural bitumen in known accumulations plus 917 billion barrels of bitumen in place in the less well-known carbonate deposits. Future discoveries of deposits on the scale of the Orinoco Oil Belt are not expected to be found but additional large exploitable natural bitumen deposits are known in the Russian Federation, the United States, and elsewhere. Relatively small portions of the two major deposits are currently being produced, but this annual production is increasing rapidly. Current exploitation projects in Canada alone suggest a rise in bitumen production from about 750,000 b/d in 2003 to more than three million b/d within this decade. It is not likely that any other petroleum energy source offers a greater supply potential for the future.

The largest extra-heavy oil and natural bitumen deposits occur in platform deposits of sediments, which lap out against continental cratons. Due to uplift and erosion their truncated, up-dip edges the originally mobile oil has been exposed to degradation, principally bacterial, resulting in the high densities and viscosities characteristic of extra-heavy oil and natural bitumen. The densities and viscosities are directly related to their origin as the degraded residues of conventional oils. This has resulted in a large increase in content of polar molecules, of which the asphaltenes are the largest and most troublesome. They plug the pores of the reservoir rocks, contain the bulk of the trace elements, and resist breakdown in the refinery to smaller and atomically lighter molecules.

Highly innovative advances in reservoir extraction technology have increased attainable production rates and reduced costs. Further reductions in production and refining costs are a necessary next step to substantially increase their role in supply.