The world depends on fossil fuels for its energy, and the United States is no exception. The vast majority of U.S. energy — more than 80 percent in 2009 — comes from burning fossil fuels.

Crude oil, coal and natural gas formed from the prehistoric matter of plants, animals, zooplankton and other life that was buried sometimes miles deep inside the Earth and subjected to high temperatures and high pressure over millions of years. These three so-called fossil fuels include a wide assortment of carbon-based substances.



Humans have been using coal as a fuel for hundreds or even thousands of years, and coal fueled steam engines in trains long before the liquid fuel-powered engines of today’s cars were in use.

Coal is the most abundant fossil fuel in the United States, according to the U.S. Energy Information Administration. It’s cheap, readily mined domestically, and generated almost half of all electricity in the country in 2009 as well as more than 40 percent of electricity produced globally. Though American coal is a domestic affair — we don’t need to import it — the fuel has caused substantial air pollution, as well as ground and surface water pollution from mercury and acid rain. Coal is also the source of countless mining and transportation accidents and steady supply of greenhouse gases.

Currently the United States exports more coal than it imports, but the majority of U.S. coal is produced and used domestically. In 2009, we exported about 5 percent of supply, and we imported less than half that amount, about 21 million short tons.

Like all fossil and biofuels, all coal produces carbon dioxide when it is burned. However, coal quality varies substantially based upon where it is mined. Some coals can produce more energy per pound, and each source of coal has naturally-occurring pollutants that can be released when the coal is burned or stored, including radioactive materials and toxic metals like mercury. Coal-fired power plants produce small particulates — tiny dusts — that can harm lungs, as well as sulfur and nitrogen compounds that cause acid rain. Modern U.S. coal plants are required to have scrubbers that cut down the amount of pollution. This requirement isn’t necessarily the case in other countries. Currently mercury-specific scrubbers aren’t required, but sulfur scrubbers do reduce mercury content. Mercury can otherwise end up in waterways and oceans, building up in living matter like the fish we eat.

In coal-fired power plants, the coal is burned to heat water into steam. The steam runs turbines to produce electricity, while the smoke from the coal fire is filtered to remove particulates and other pollutants.



Humans have known about petroleum, or crude oil, for centuries, but the substance wasn’t considered terribly interesting until the mid 1800s, when it was distilled into kerosene and found to be a good, cheap alternative to burning whale oil in oil lamps. At that time, only the wealthiest could afford whale oil, which was preferred over candles or animal fats. Americans and others worldwide quickly adopted petroleum and learned to make an unending stream of useful products from it. Simultaneously, a worldwide obsession with striking oil was born.

The earliest combustion engines were invented before gasoline, diesel or kerosene, but automobiles started becoming available by the late 1800s, a few decades after petroleum exploration began in earnest.

The U.S. measurement of a barrel of oil, 42 gallons, originates from oil fields in Pennsylvania, when oil companies stored petroleum in whiskey barrels.

Petroleum Production, Consumption, and Marketing

Today, more than two-thirds of U.S. petroleum consumption is used for transportation. In 2009, petroleum fuel was the single largest source of energy in the United States, with 18,690,000 barrels per day providing 37 percent of energy.  Petroleum use contributed 43 percent of 2009 energy-related carbon dioxide emissions, according to the U.S. Energy Information Administration.

The United States is the world’s third largest crude oil producer. We produce oil in 31 states and offshore. The top three oil-producing states are Texas, Alaska, and California.

The United States produces a large amount of crude oil, and it imports just as much, or more. In 2009, we imported 51 percent of the oil we used. We are the world’s largest consumer of petroleum and in 2009 we consumed 22 percent of the world’s petroleum.

Of petroleum imported to the United States, half is imported from various countries in the North, South and Central America and the Caribbean.

A graph of consumption, production and imports can be found here for 1950 through 2009.

Crude oil prices are defined by the type and source of the oil. In the United States, two common indices for oil prices are the West Texas Intermediate and Brent Crude.

Oil is sold by both investor-owned corporations and national, also called state-owned, companies. The United States has no state-owned oil companies. However, state-owned companies are responsible for more than half of the global oil production, and they hold the lion’s share of the world’s proven oil reserves, over 80 percent in 2007. Pie chart here.


The largest state-owned oil companies include:


Major investor-owned companies include:


The Organization of Petroleum Exporting Countries, commonly called OPEC, collaborate to control oil supply and prices. OPEC includes: Algeria, Angola, Libya, Nigeria, Qatar, Iran, Iraq, Kuwait, Saudi Arabia, United Arab Emirates, Ecuador, Venezuela.


Refining and chemical processing of petroleum and natural gas, plastics

Today, crude oil is refined and transformed into so many products it might be simpler to list the products that don’t use oil. The most direct derivatives of petroleum include diesel and jet fuel, and gasoline. In 2009, less than 7 percent of crude oil became non-fuel goods, from artificial food coloring to asphalt and plastics.

One major product of petroleum is naphtha, a raw material for petrochemicals used to make things found on almost every store shelf. That’s because naphtha can form the building blocks for polyethylene and polypropylene, two widely-used plastics found in packaging, chairs, textiles and even medical implants. Natural gas and petroleum are also used to make a countless array of other solvents, waxes, and non-food alcohols.

More than half the price of gasoline or diesel is from buying the crude oil, and the rest is split between refining, distribution and marketing, and taxes, according to 2011 statistics compiled by the Energy Information Administration. For more information about the price of gasoline, go here.


Petroleum transportation

Oil is transported in large quantities through long-distance pipelines and by giant oil tankers. The strait of Hormuz, a hairpin-shaped waterway between Iran and Oman, saw more that 15 million barrels of oil pass through it daily in 2009. Because so much oil has to travel through such a limited space, the strait is called a chokepoint. Other noteworthy oil chokepoints include the Straits of Malacca between Indonesia, Malaysia, and Singapore, and the Suez Canal, in Egypt. The Panama Canal is not a major oil chokepoint, as many of today’s tankers are too large to pass through it.

Piracy of large tankers has been an issue in recent years, particularly along chokepoints where pirates know tankers will pass.

Most U.S. oil and petroleum products is also transported through more than 160,000 miles of oil pipelines criss-crossing the country, as well as connecting into Canada and Mexico, according to the Association of Oil Pipelines.



Natural Gas History

During the 19th century, some types of lamps ran on natural gas, usually along city streets. In 1885 Robert Bunsen invented the Bunsen burner, which mixes gas with air to produce a steady flame for heat or cooking.

Widespread household use of natural gas waited until the mid-twentieth century, when thousands of miles of natural gas pipelines were built across the country.

Today, natural gas is a popular fuel for heating homes, cooking, and powering clothes dryers, as well as for power plants and industries. Some vehicles are powered by natural gas as well. Like petroleum, natural gas is a starting material for many other goods like plastics, chemicals, and even hydrogen.

Natural gas is an especially efficient fuel when burned in combined-cycle power plants, where electricity is produced in two stages. The combusted natural gas itself runs gas turbines, and then the leftover heat is used to heat water for steam-turbines.

In recent years, geologists have revised upwards their ideas of how much natural gas we can recover, increasing estimates by 11 percent between 2008 and 2009 alone, though there has been some contention that these estimates are inflated.


Natural Gas Production, Refining and Consumption

Unlike petroleum, most of the natural gas consumed in the United States is produced here too. A small amount is imported, mostly from Canada, which provided nearly 88 percent of imported gas in 2010. Trinidad, Tobago, Egypt, Norway, Nigeria, and Qatar also provide a small amount of the natural gas supply in the form of shipped liquefied natural gas.

Domestically, natural gas is transported by pipelines. For a map of this network, see here.

Liquefied natural gas, commonly called LNG, is created solely to make it easier to transport natural gas. The gas turns to liquid at -260 degrees Fahrenheit, and requires far less volume to store, about 600 times less space. However, liquefying requires refrigeration and the location receiving the liquefied gas must have special facilities.


Sources of natural gas

Natural gas is made of mostly of methane, with some other, similar carbon-based gases mixed in. In addition to being trapped underground, methane, a greenhouse gas, is emitted from manure and agricultural waste. These sources can also be captured and burned for energy. Furthermore, some agricultural wastes can be broken down to release methane through anaerobic digestion.

After the gas is captured — from drilling or other source — it’s separated to remove water and unwanted gases, which are released or burned off. Then the gas is compressed and stored, or combined with something to make it smell bad — for safety — and piped as a source of energy for consumption by industries, business, homes, and power plants.  However, a small proportion of natural gas is also used by the petrochemical industry to make antifreeze, plastics, dyes, explosives, paint, fertilizers, and medicines.


Gas deposits in shale and hydrofracking

While burning natural gas is far cleaner than coal or petroleum, drilling for natural gas has raised concerns in recent years as companies have ramped up the use of hydraulic fracturing, or “fracking,” to get at shale gas. It’s too expensive to plumb natural gas deposits that are trapped in shale with conventional methods. Instead, high volumes of a mixture of water, chemicals and sand are pumped into deep wells at high pressure, inducing fissures in the underground rock, through which the trapped gas can be released and collected. Conventional gas drilling requires a company to drill all the way down to where the gas is located, while “fracking” allows companies to access more gas for less cost as the drill doesn’t need to go all the way to all the individual locations of the gas. A diagram of hydraulic fracturing can be found here.

Fracking requires a lot of water, which has to be treated after it’s used, and any leaks can lead to contamination of ground water and drinking water with a variety of chemicals. Even though the use of fracking has been contentious in several states, the industry is rapidly expanding.

In 2009, most natural gas, 86 percent of it, came from non-shale sources. However, shale gas is expected to constitute almost half of the U.S. natural gas supply by 2036, according to the U.S. Energy Information Administration.

Historical and projected sources of natural gas are graphed here.

Wet Natural Gas Proved Reserves by area 2009