Geochemist Steve Larter and his colleagues may have found a way to drive energy production from the world's diminishing oil supplies that minimizes damage to the environment. And the process might even be agreeable to the oil industry.

Humans are not the only organisms reliant on Earth's oil supplies. Bacteria found in oil reservoirs both at Earth's surface and below it degrade oil, turning it into a viscous substance that makes recovery and refining more costly and difficult.

Geologists have long known about these oil-degrading microorganisms, but how they go about their business in subsurface oil reservoirs has been a matter of debate. Several studies suggested that oil in these reservoirs is degraded by oxygen-dependent 'aerobic' bacteria using oxygen in meteoric groundwater. But degraded oil has also been found in places with no direct access to oxygen-rich surface water.

Under an oil-industry-funded project called 'Bacchus' (, Larter, of the University of Calgary in Canada, and his colleagues discovered that anaerobic microorganisms can degrade oil hydrocarbons by fermentation, producing methane as a byproduct.

These organisms react water with hydrocarbons in the oil to produce acetic acid, hydrogen and carbon dioxide; they then combine the H2 and CO2 to form methane. “It's literally oil plus water equals life and a little gas,” says Larter.

Larter says the work was inspired by a 1999 Nature paper (K. Zengler et al. Nature 401, 266–269; 1999). On the basis of results from lab experiments, Zengler and his colleagues had proposed a mechanism for near-surface hydrocarbon degradation by anaerobic microbes.

“Their basic mechanism was broadly correct, but was subtly wrong for subsurface oil reservoirs,” says Larter. His team used a combination of microbiological studies, laboratory oil-degradation experiments and case studies from the oilfields of the North Sea, South America, China and western Canada. The western Canadian fields are home to one of the world's largest accumulations of biodegraded oil (see page 176).

At present, the oil industry could use this knowledge of how biodegradation works to predict and target where the less-biodegraded oil is located within reserves. Taking oil from these areas would decrease the use of energy-costly recovery processes, such as steam-assisted gravity drainage, which uses steam to melt oil from reservoir rocks.

But in future, the work of Larter's team could dramatically change the energy-recovery process. The methane produced by the oil-degrading microorganisms provides the same amount of energy as oil, but emits less CO2 when burned. And the intermediate H2 — described by Larter as “the holy grail” of alternative energy because it is hard to produce cheaply, but carries no carbon signature — could also be used as fuel.

“If the process could be accelerated and methane or H2 recovered from oilfields at economic rates, this could be a way for the oil industry to keep doing what it's doing, but move easily and quickly to lower carbon emission energy-recovery routes,” he says. Although he admits that at the moment this “seems like a very long shot”.

With these prospects still far off, Larter is doing his best to reduce his own carbon footprint. He walks to work and uses public transport. “I wear out lots of boots,” he says.