The data from which these carbon-emissions estimates were derived are values of fuel consumed: in billions of cubic feet, for natural gas; in millions of barrels, for petroleum products; and in thousands of short tons, for coal. The resulting emissions estimates are expressed as teragrams of carbon. A teragram is 1012 grams, or 106 metric tons. To convert from carbon to carbon dioxide, multiply by 44/12 (=3.67). Data are available for over 30 different petroleum products, with the exact breakdown varying somewhat from year to year. These products have been treated separately here until the final step of the estimation, at which time CO2 emissions were summed and attributed to liquid petroleum products. These fuel-consumption data are available from the Energy Information Administration of the U.S. Department of Energy. They are published in the Monthly Energy Review, and are available electronically from the Energy Information Administration.