The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

Most direct uses of primary energy are limited to generating heat and motion. Electricity, by contrast, is extremely versatile, with a wide range of complex applications. 

Most direct uses of primary energy are limited to generating heat and motion. Electricity, by contrast, is extremely versatile, with a wide range of complex applications. 

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

A few industries use a very large share of energy in the industrial sector. Petroleum refining is the principal consumer, with the chemical industry a close second. Those users, plus the paper and metal industries, account for 78% of total industrial energy use.

Current trends indicate that by 2040 residential buildings will consume up to 28% less energy for heating but about 50% more for cooling. 

Current trends indicate that by 2040 residential buildings will consume up to 28% less energy for heating but about 50% more for cooling. 

A typical incandescent lamp (traditional light bulb) that consumes 60 watts of power produces around 800 lumens. A compact fluorescent lamp emits the same amount of light while using only 13 watts. And an LED lamp consumes only 10 watts to give off the same 800 lumens.

A typical incandescent lamp (traditional light bulb) that consumes 60 watts of power produces around 800 lumens. A compact fluorescent lamp emits the same amount of light while using only 13 watts. And an LED lamp consumes only 10 watts to give off the same 800 lumens.

A typical incandescent lamp (traditional light bulb) that consumes 60 watts of power produces around 800 lumens. A compact fluorescent lamp emits the same amount of light while using only 13 watts. And an LED lamp consumes only 10 watts to give off the same 800 lumens.

Improved vehicle efficiency has allowed for increases in weight, horsepower and fuel economy.

Improved vehicle efficiency has allowed for increases in weight, horsepower and fuel economy.

Improved vehicle efficiency has allowed for increases in weight, horsepower and fuel economy.

U.S. energy consumption was about 98 quads in 2014.

U.S. energy consumption was about 98 quads in 2014.

U.S. energy consumption was about 98 quads in 2014.

In 2014, the United States got 35% of its energy from petroleum, and experts project that demand for this fuel will rise at least through 2020. 

In 2014, the United States got 35% of its energy from petroleum, and experts project that demand for this fuel will rise at least through 2020. 

In 2014, the United States got 35% of its energy from petroleum, and experts project that demand for this fuel will rise at least through 2020. 

With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.

With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.