"We found that none of the publicly available studies done to date on greenhouse-gas emissions associated with the production and use in automobiles of oil-sands-derived fuels are sufficient to properly characterise the life cycle performance of these fuels," MacLean told environmentalresearchweb.

Indeed, the new results show large differences in greenhouse-gas emissions between these different studies.

MacLean's team critically reviewed and compared all publicly available life cycle studies and models that calculate the greenhouse-gas emissions associated with producing bitumen and/or crude oil from oil sands in Alberta, Canada. The researchers ensured that the studies were as similar as possible, to make rigorous comparisons easier.

Canada ranks second largest in terms of global proven crude oil reserves (around 15% of world reserves) after Saudi Arabia, explained MacLean. Most of these reserves are found in Alberta's oil sands – more than 173 billion barrels' worth – and Canada is the largest exporter of oil to the US.

According to Alberta Energy, oil-sands production reached more than 1.2 million barrels a day in 2006 and accounted for around 42% of Canada's total crude output. At this time, the total primary production produced in Canada was 16.8 million Terajoules, of which 6 million TJ was crude oil. From Statistics Canada, oil sands account for about 15% of Canada's energy production.

Oil sands are composed of sands, clay, water and bitumen; it is the bitumen that is used in energy production. This substance is heavy, viscous and does not flow at room temperature, unlike conventional crude oil.

Extracting bitumen from sand requires a lot of energy because it is mined, crushed and separated with hot water or steam. What's more, bitumen is generally upgraded into a lighter synthetic crude oil, which is another energy-intensive process.

MacLean said that her team's work is already helping policy makers, particularly in California and other states developing life cycle-based low-carbon fuel standards, to improve emissions estimates so that they more accurately reflect the reality of oil-sands pathways. "We believe that this work will contribute to a fairer and more scientifically-based comparison between oil-sands-derived fuels, conventional crude oil-derived fuels and alternatives, such as biofuels," she added. "Our work will also inform oil-sand industry decision makers in their operational and future technology choices, as well as motivate analysts to conduct high-quality studies in this area."

The team is now developing its own life cycle models of oil-sands technologies. "We are working closely with the industry and government to generate ranges of emissions factors that characterise the current oil-sand industry," explained MacLean. "We are also extending our approach to analyse emerging technologies and to include metrics other than greenhouse gases – for example, land use and water consumption."

The researchers reported their work in Environmental Research Letters.