Carbon emissions associated with extracting tar sands could increase over time, as in-situ mining—which creates more emissions than surface mining—is used to extract bitumen located deeper and deeper in the earth. Tar sands also impact water supplies. For every gallon of gasoline produced by tar sands, about 5.9 gallons of freshwater are consumed during the extraction, upgrading, and refining process. That’s roughly three times as much as used for conventional oil.