This page contains a short description of the fossil fuels and their origins. There is also a diagram of waht can be derived from a barrel of oil and there are some conversion factors relating to the fossil fuels' energy and carbon content.


Where Fossil Fuels Come From

There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds of millions of years ago before the time of the dinosaurs - hence the name fossil fuels. The age they were formed is called the Carboniferous Period. It was part of the Paleozoic Era. "Carboniferous" gets its name from carbon, the basic element in coal and other fossil fuels.

The Carboniferous Period occurred from about 360 to 286 million years ago. At the time, the land was covered with swamps filled with huge trees, ferns and other large leafy plants. The water and seas were filled with algae - the green stuff that forms on a stagnant pool of water. Algae are actually millions of very small plants.

Some deposits of coal can be found during the time of the dinosaurs. For example, thin carbon layers can be found during the late Cretaceous Period (65 million years ago) - the time of Tyrannosaurus Rex. But the main deposits of fossil fuels are from the Carboniferous Period. For more about the various geologic eras, go to

As the trees and plants died, they sank to the bottom of the swamps of oceans. They formed layers of a spongy material called peat. Over many hundreds of years, the peat was covered by sand and clay and other minerals, which turned into a type of sedimentary rock.

More and more rock piled on top of more rock, and it weighed more and more. It began to press down on the peat. The peat was squeezed and squeezed until the water came out of it and it eventually, over millions of years; it turned into coal, oil or petroleum, and natural gas.



Coal is a hard, black colored rock-like substance. It is made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulfur. There are three main types of coal - anthracite, bituminous and lignite. Anthracite coal is the hardest and has more carbon, which gives it higher energy content. Lignite is the softest and is low in carbon but high in hydrogen and oxygen content. Bituminous is in between. Today, the precursor to coal - peat - is still found in many countries and is also used as an energy source.

The earliest known use of coal was in China. Coal from the Fu-shun mine in northeastern China may have been used to smelt copper as early as 3,000 years ago. Coal is found throughout the world. Coal is mined out of the ground using various methods. The coal is then shipped by train and boats and even in pipelines. In pipelines, the coal is ground up and mixed with water to make what's called a slurry. This is then pumped many miles through pipelines. At the other end, the coal is used to fuel power plants and other factories.


Oil or Petroleum

Oil is another fossil fuel. It was also formed more than 300 million years ago. Some scientists say that tiny diatoms are the source of oil. Diatoms are sea creatures the size of a pin head. They do one thing just like plants; they can convert sunlight directly into stored energy.

As the diatoms died they fell to the sea floor. Here they were buried under sediment and other rock. The rock squeezed the diatoms and the energy in their bodies could not escape. The carbon eventually turned into oil under great pressure and heat. As the earth changed and moved and folded pockets where oil and natural gas can be found were formed.

Oil has been used for more than 5,000-6,000 years. The ancient Sumerians, Assyrians and Babylonians used crude oil and asphalt ("pitch") collected from large seeps on the Euphrates River. A seep is a place on the ground where the oil leaks up from below ground. The ancient Egyptians, used liquid oil as a medicine for wounds, and oil has been used in lamps to provide light.

The Dead Sea used to be called Lake Asphaltites. The word asphalt was derived is from that term because of the lumps of gooey petroleum that were washed up on the lake shores from

Over time the demand for oil continued to increase as a fuel for lamps. Petroleum oil began to replace whale oil in lamps because the price for whale oil was very high. During this time, most petroleum oil came from distilling coal into a liquid or by skimming it off of lakes.

Then on August 27, 1859, Edwin L. Drake struck liquid oil at his well near Titusville, Pennsylvania. He found oil under ground and a way that could pump it to the surface. The well pumped the oil into barrels made out of wood. This method of drilling for oil is still being used today all over the world in areas where oil can be found below the surface.

Oil and natural gas are found under ground between folds of rock and in areas of rock that are porous and contain the oils within the rock itself. The folds of rock were formed as the earth shifts and moves. To find oil and natural gas, companies drill through the earth to the deposits deep below the surface. The oil and natural gas are then pumped from below the ground by oil platforms. They then usually travel through pipelines or by ship.

The diagram shows what can be derived from a barrel of crude oil. Oils from different regions have contain slightly different amounts of the various hydrocarbons.

One barrel contains 42 US gallons [35 UK gallons] of crude oil. The total volume of products made is 44.2 GALLONS - 2.2 gallons greater than the original 42 gallons of crude oil. This is called "processing gain," where other chemicals are added to the refining process to create the products.

The ~2.8% of the content labelled 'feedstocks' are the basis of the organic chemical industry. As the reserves of oil diminish as they must do, sufficient stocks of oil-for-chemistry need to be ensured.


Oil is stored in large tanks until it is sent to various places to be used. At oil refineries, crude oil is split into various types of products by heating the thick black oil.

Oil is made into many different products - fertilizers for farms, the clothes you wear, the toothbrush you use, the plastic bottle that holds your milk, the plastic pen that you write with. They all came from oil. There are thousands of other products that come from oil. Almost all plastic comes originally from oil.

The products include gasoline, diesel fuel, aviation or jet fuel, home heating oil, oil for ships and oil to burn in power plants to make electricity. Here's what a barrel of crude oil can make.

Natural Gas

Sometime between 6,000 to 2,000 years BCE (Before the Common Era), the first discoveries of natural gas seeps were made in Iran. Many early writers described the natural petroleum seeps in the Middle East, especially in the Baku region of what is now Azerbaijan. The gas seeps, probably first ignited by lightning, provided the fuel for the "eternal fires" of the fire-worshiping religion of the ancient Persians.

Natural gas is less dense than air. Natural gas is mostly made up of methane, CH4. Natural gas is usually found near petroleum underground. It is pumped from below ground and travels in pipelines to storage areas.

Natural gas usually has no odour and is colourless. Before it is sent to the pipelines and storage tanks, it is mixed with organic sulfides that give it a strong odour. The odour makes it easy to smell if there is a leak.

Some conversion factors

Natural gas quantities are usually quoted as cubic feet at one atmosphere pressure. One cubic foot = 0.283 cubic metres and contains 53.5 grams of carbon.


Oil supplies are usually quoted as barrels. One barrel has a volume of oil of 159 litres [cubic decimetres]. 7.3 barrels contain one metric tonne [1000 kg] of oil.

Coal supplies are usually quoted in tonnes.

The carbon [tonnes] and energy content [gigaJoules, giga = 109] of one tonne of each of the fossil fuels are given in the table below.

Values for one tonne of fuel Carbon/t Energy/GJ
Natural Gas 0.75 50.2


0.84 41.6
Coal 0.85 26.0