This paper reviews microbial interactions with heavy oil and identifies promising areas for research and development of new biotechnology for facilitating the exploitation of heavy-oil resources.

Microbial degradation of heavy crudes occurs rapidly only where O₂ is available. Biodegradation results in the preferential removal of simple alkanes and aromatics to yield a more viscous final crude that is close to a bitumen in its chemical composition. There is little evidence for the buildup of partially oxidized fractions in the crude.

Microbial growth on heavy oil is often accompanied by the emulsification of the oil because of the production of biosurfactants.

Although the use of soil microorganisms as an indicator for heavy oil is not likely to become an important exploration tool in North America, a number of heavy-oil applications hold some promise for future biotechnology. These include microbially enhanced oil recovery, flow diversion, and water control in situ through selective plugging, deemulsification of stubborn EOR production emulsions, organic sulfur removal, viscosity reduction for pipelining, and miscellaneous surfactant applications for cleaning purposes, cold-water oil sands separation, etc.