Each Gallon Of Gas Requires 98 Tons Of Plants

by Lee Siegel/ University of Utah

"Can you imagine loading 40 acres worth of wheat -- stalks, roots and all -- into the tank of your car or SUV every 20 miles?" asks ecologist Jeff Dukes, whose study was published in the November issue of the journal Climatic Change.

But that's how much ancient plant matter had to be buried millions of years ago and converted by pressure, heat and time into oil to produce one gallon of gas, Dukes concluded.

Dukes also calculated that the amount of fossil fuel burned in a single year -- 1997 was used in the study -- totals 97 million billion pounds of carbon, which is equivalent to more than 400 times "all the plant matter that grows in the world in a year," including vast amounts of microscopic plant life in the oceans.

"Every day, people are using the fossil fuel equivalent of all the plant matter that grows on land and in the oceans over the course of a whole year," he adds.

In another calcultation, Dukes determined that "the amount of plants that went into the fossil fuels we burned since the Industrial Revolution began [in 1751] is equal to all the plants grown on Earth over 13,300 years."

Explaining why he conducted the study, Dukes wrote: "Fossil fuel consumption is widely recognized as unsustainable. However, there has been no attempt to calculate the amount of energy that was required to generate fossil fuels, (one way to quantify the 'unsustainability' of societal energy use)."

Dukes' study -- published in the November issue of the journal Climatic Change -- offers numerous calculations to determine how much plant matter buried millions of years ago was required to produce the oil, natural gas and coal consumed by modern society, which obtains 83 percent of its energy needs from fossil fuels.

Using published biological, geochemical and industrial data, he estimated the amount of photosynthetically fixed and stored by ancient plants carbon that was required to form the coal, oil and gas that we are burning today.

The ecologist calculated that 4.87 kilograms of oil are needed to make a gallon of gasoline. Oil is 85 percent carbon, Dukes says, therefore 4.14 kilograms of carbon are needed to make enough oil to produce one gallon of gasoline.

He explains that because a very low percentage of the original carbon in ancient plant material actually ends up as oil, it takes some 98 tons -- 89 metric tons -- to produce one gallon of gasoline.

"It took an incredible amount of plant matter to generate the fossil fuels we are using today," says Dukes. "The new contribution of this research is to enable us to picture just how inefficient and unsustainable fossil fuels are -- inefficient in terms of the conversion of the original solar energy to fossil fuels."