What’s in a Gallon of Gas?

Everyone knows fossil fuels come from long-dead plants, but Jeffrey Dukes wanted real numbers: How much plant matter does it take to make a gallon of gasoline? Dukes, a biologist, ecologist, and dabbler in biogeochemistry at the University of Massachusetts, discovered that such statistics are hard to find. So he decided to figure them out for himself and was surprised by the answers. A gallon of gas represents roughly 100 tons of plant matter, the amount that exists in 40 acres of wheat. Burning that gallon puts 20 pounds of carbon dioxide into the air. The annual consumption of gasoline in the United States, about 131 billion gallons of gas, is equivalent to 25 quadrillion pounds of prehistoric biomass and releases some 2.6 trillion pounds of carbon dioxide. The numbers are even more sobering when you consider all the fossil fuels—coal, natural gas, and oil—that people consume. Since 1751, roughly the start of the Industrial Revolution, humans have burned the amount of fossil fuel that would have come from all the plants on Earth for 13,300 years. “We know that fossil-fuel use is not sustainable in the long run,” Dukes says. “This study will, I hope, encourage people to face up to the energy problem now.”