Inside Climate News - The average "energy returned on investment" for conventional oil is roughly 25:1. In other words, 25 units of oil-based energy are obtained for every one unit of other energy that is invested to extract it.
Tar sands retrieved by surface mining has an EROI of only about 5:1, according to [new] research. Tar sands retrieved from deeper beneath the earth, through steam injection, fares even worse, with a maximum average ratio of just 2.9 to 1. That means one unit of natural gas is needed to create less than three units of oil-based energy.
"They have to use a lot of natural gas to upgrade this heavy, sticky, gooky almost tar-like stuff to make it fluid enough to use," said Charles Hall, a professor at the State University of New York's College of Environmental Science and Forestry. Hydrogen from gas heats the tar sands so the viscous form of petroleum it contains, known as bitumen, can be liquefied and pumped out of the ground. In this way, Hall said, gas helps turn tar sands "into something a bit closer to what we call oil."