In fact, they burn natural gas to extract oil. Not oil for oil.
Three barrels of natural gas (at $7/barrel) are burned to extract one of oil (at what, $60 a barrel now).
Net greenhouse gasses increase, but looked at only due to costs of oil and natural gas, it's a money maker and will continue to be until price of natural gas is raised, either through supply/demand, or better, through carbon tax.