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.

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.

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

The most recent federal efficiency standards, finalized by the U.S. National Highway Traffic Safety Administration (NHTSA) and the Environmental Protection Agency (EPA) in 2012, are projected to increase fuel economy to the equivalent of 54.5 mpg for cars and light-duty trucks by model year 2025, while also reducing CO2 emissions. 

The United States emits about 18% of the world’s greenhouse gases, behind only China, which accounts for approximately one-quarter of total global emissions. 

The United States emits about 18% of the world’s greenhouse gases, behind only China, which accounts for approximately one-quarter of total global emissions. 

The United States emits about 18% of the world’s greenhouse gases, behind only China, which accounts for approximately one-quarter of total global emissions. 

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

By far the largest share of energy in transportation is consumed by cars, light trucks, and motorcycles—about 58% in 2012, followed by other trucks (21%), aircraft (9%), boats and ships (3%), and trains and buses (3%). Pipelines account for 3% and military uses for 2%.

Fuel cells are an efficient way to convert hydrogen to electricity, but the energy is stored in the hydrogen.

On average, even after passing through hundreds of kilometers of air on a clear day, solar radiation reaches Earth with enough energy in a single square meter to run a mid-size desktop computer-if all the sunlight could be captured and converted to electricity.

On average, even after passing through hundreds of kilometers of air on a clear day, solar radiation reaches Earth with enough energy in a single square meter to run a mid-size desktop computer-if all the sunlight could be captured and converted to electricity.

There is no silver bullet. Tomorrow’s energy, like today’s, will come from a variety of sources.

There is no silver bullet. Tomorrow’s energy, like today’s, will come from a variety of sources.

There is no silver bullet. Tomorrow’s energy, like today’s, will come from a variety of sources.