Assume that you have been assigned the responsibility of purchasing fuel for a large electric utility company.
The 1993 average prices of fuel delivered to electric utilities were $28.58 per short ton of coal,
$15.42 per 42-gallon barrel of oil, and $2.62 per thousand cubic feet of natural gas.
Tons, barrels, cubic feet--how do you compare apples and oranges?
To make meaningful comparisons of energy commodities, you must convert physical units of measure (such as weight or volume) and the energy content of each fuel to comparable units.
One practical way to compare different fuels is to convert them into British thermal units (Btu).
The Btu is a precise measure of energy--the amount of energy required to raise the temperature of 1 pound of water 1 degree Fahrenheit. (See Table of conversion factors)
A single Btu is insignificant in terms of the Nation's energy consumption, or even in terms of energy use in a
single household. One Btu is approximately equal to the energy released in the burning of a wood match.
The average single-family household consumed 98 million Btu of energy in a recent year.
So on the family level, 1 million Btu is a meaningful quantity.
Billions, trillions, and quadrillions of Btu are used to measure quantities of energy larger than those
consumed by typical households. (Written out, 1 quadrillion is a 1 and 15 zeros.) To put those quantities in
perspective, 1 million Btu equals about 8 gallons of motor gasoline. One billion Btu equals all the electricity
that 30 average Americans use in 1 year. One trillion Btu is equal to 474 100-ton railroad cars of coal intended
for electric utilities. And 1 quadrillion Btu is equal to 470 thousand barrels of oil every day for 1 year. In
1993, the Nation used 84 quadrillion Btu of energy: 34 quadrillion Btu of petroleum, 21 quadrillion Btu of
natural gas, 19 quadrillion Btu of coal, and 10 quadrillion Btu of other energy sources. British thermal units
are useful for more than just calculating volumes of consumption. Price equivalents are usually expressed in
cents per million Btu, and the homeowner often thinks of Btu in terms of dollars and cents. In 1993, a ton of
coal used to generate electricity cost more than twice as much as a barrel of oil. The barrel of oil, however,
contained about 6.2 million Btu, while the ton of coal contained 21 million Btu, over three times as much energy.
On a Btu basis, coal was cheaper. (Of course, cost is not the only consideration in selecting a fuel.
Environmental restrictions, equipment costs, and other factors must also be taken into account.)
By use of the Btu, it is possible to compare prices not only for different forms of fuel, but also for
different products from the same fuel. For example, motor gasoline contains an average of 5.25 million Btu per
barrel, while jet fuel (kerosene-type) contains 5.67 million Btu per barrel. At $31.88 per barrel for motor
gasoline and $24.32 per barrel for jet fuel in 1993, motor gasoline costs $6.07 per million Btu and jet fuel
costs $4.29 per million Btu. By itself, a single Btu does not mean very much. For the average consumer who
uses millions of Btu per year, however, it is a term well worth knowing.
More information on this subject can
be found in the following EIA publications: Monthly Energy Review, Annual Energy Review,
State Energy Data Report, Household Energy Consumption and Expenditures,and Cost and Quality of Fuels for
Electric Utility Plants.
