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Definition of fossil fuel

Definition of fossil fuel

Fossil fuels are non-renewable energy resources because they require millions of years for their formation in a natural way. Due to their high calorific power they are useful energy sources to generate thermal energy and their use has allowed the great economic and demographic growth linked to the industrial revolution of the 19th century. Although now they are fundamental for our economy. In 2007, the combustion of coal, oil and natural gas accounted for 86.4% of the world's primary energy. However, its combustion is one of the main sources of atmospheric pollution and global warming, which is an important problem of desostenibilitat.

They originated naturally due to a fossilization process in environmental anoxia (lack of oxygen): the organic matter has not been degraded by microorganisms (which can not live), becoming carbon dioxide (CO2) and water (H2O), but it remains in the form of more complex organic molecules, solid, liquid or gas, the energy of which is released in using them as fuel.

Definition of fossil fuel

There are several definitions of fossil fuel. From our point of view, a definition that best reflects what a fossil fuel is is the following:

Fossil fuels are those fuels originated by the partial decomposition of organic matter millions of years ago transformed by the pressure and temperature due to the layers of sediments accumulated on it.

By definition, fossil fuels are considered non-renewable energy sources; the consumption of this fuel is much higher than the time it takes to generate (millions of years).

Types of fossil fuels

The main examples of fossil fuels are oil, coal and natural gas.


Petroleum is a mineral oil, constituted by hydrocarbons, contained in large bags to the upper strata of the earth's crust. This fossil fuel, once refined, gives a large quantity of products used as an energy source (gasoline, diesel, fuel, etc.) or as a raw material for the petrochemical industry.

This type of fuel is widely used in thermal engines, especially in automotive engines. Today, in this type of applications, cars with electric motor is developing very quickly. The advantage of electric motors is that energy can be generated through renewable energy sources.


Coal is an example of fossil fuel

Coal is a black sedimentary rock, very rich in carbon and with varying amounts of other elements, mainly hydrogen, sulfur, oxygen and nitrogen. Most of the coal was formed during the Carboniferous period (from 359 to 299 million years ago).

The use of coal was of vital importance during the industrial revolution, where it was the main source of energy for the industry. Nowadays, its use has been reduced considerably among other reasons to reduce the greenhouse effect.

Natural gas

Natural gas is a source of fossil energy, like coal or oil. It is constituted by a mixture of hydrocarbons, molecules formed by carbon and hydrogen atoms. Its calorific value varies greatly according to its composition, but the highest are between 8,500 and 10,200 kilocalories per cubic meter of natural gas.

Natural gas is a primary energy (it can be obtained directly without transformation). The other primary energies are solar energy, coal and oil. It is the cleanest fossil energy in terms of waste and atmospheric emissions, and the most efficient fuel for obtaining electricity in thermal power plants, with a total efficiency of 50.7% compared to 25.7% of fuel, 26.1% of the uranium (nuclear power plant) and 26.8% of the coal.

Its direct use, without having to previously transform into electricity, has a much higher efficiency of 91.2%. It is also cheaper and easier to store than coal and petroleum products.

For all these reasons, it began to be used as a preferred fuel starting in the 1960s, except for transportation, where oil continues to predominate. In addition, it is also used as a raw material for many chemical products.

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Last review: April 13, 2017