As the biggest and most accessible reservoirs of light crude oil supplies are depleted, the oil industry has increasingly been turning to so-called "unconventional" stocks -- heavy, viscous feedstock and tar sands, ScienceNews.org reported last week.
More and more oil being processed by U.S. refineries is of this "heavy" variety, requiring more work -- and more energy -- to produce the gasoline, diesel and other high-value fuels that power engines the world over, says Greg Karras of Communities for a Better Environment in Oakland, Calif.
Karras analyzed the publicly available data reported between 1999 and 2008 by refineries accounting for 97 percent of U.S. capacity about what types of crude oil they were refining and in what amounts.
He compared this data with the energy intensity required by processing steps used to refine and upgrade various crudes into particular products.
The move to more viscous petroleum sources "drove a 39 percent increase in emissions across regions and years," Karras says in a paper for the journal Environmental Science & Technology.
This reliance of super-viscous crude will make it difficult if not impossible to meet emission-reduction goals being presently discussed at the world climate summit in Cancun, Mexico, Karras says.
"While we talk about the need to transition to more sustainable forms of energy, actual dollar investments are increasingly skewed towards investing in more pollution intensive -- more energy intensive -- primary sources of petroleum," he says.