Recent congressional interest in U.S. energy policy has focused in part on ways through which the United States could secure more economical and reliable petroleum resources both domestically and internationally. Many forecasters identify petroleum products refined from Canadian oil sands as one possible solution. Increased production from Canadian oil sands, however, is not without controversy, as many have expressed concern over the potential environmental impacts. These impacts include emissions of greenhouse gases (GHG) during resource extraction and processing. A number of key studies in recent literature have expressed findings that GHG emissions per unit of energy produced from Canadian oil sands crudes are higher than those of other crudes imported, refined, and consumed in the United States. The studies identify two main reasons for the difference: (1) oil sands are heavier and more viscous than lighter crude oil types on average, and thus require more energy- and resource-intensive activities to extract; and (2) oil sands are chemically deficient in hydrogen, and have a higher carbon, sulfur, and heavy metal content than lighter crude oil types on average, and thus require more processing to yield consumable fuels by U.S. standards.