What Are Fossil Fuels? Definition, Types and Examples

#The three types

#Coal — the solid fossil fuel

Formed from land plants in ancient swamps. Grades run from lignite through bituminous coal to anthracite, with carbon content and calorific value rising along the sequence.

Used mainly for electricity generation and for steel making, where coal is converted to coke. India, China, the United States, Australia and Russia hold the largest reserves.

#Petroleum — the liquid fossil fuel

Crude oil, formed from marine microorganisms. On its own it is not directly usable; it is separated by fractional distillation into fractions of different boiling ranges:

Fraction	Typical use
Petroleum gas (LPG)	Cooking fuel
Petrol	Motor fuel for spark-ignition engines
Kerosene	Lamps, stoves, jet fuel base
Diesel	Trucks, buses, generators, railways
Lubricating oil	Machinery lubrication
Paraffin wax	Candles, ointments, waterproofing
Bitumen	Road surfacing

Because so many products come from one barrel — including the kerosene in lamps and jet engines — petroleum is often called "black gold" — its value lies as much in the chemical feedstock it supplies as in the fuel.

#Natural gas — the gaseous fossil fuel

Mostly methane (CH₄), typically 70–90%, with smaller amounts of ethane, propane and butane. Found in reservoirs above petroleum deposits and also in standalone gas fields.

Supplied by pipeline to homes, compressed as CNG for vehicles, or cooled to −162 °C as LNG for shipping across oceans. It burns more cleanly than coal or oil: no ash, negligible sulphur, and roughly half the carbon dioxide of coal per unit of energy.

#Everyday examples

If you want examples that are recognisable rather than categorical:

• Coal in a thermal power station generating electricity
• Petrol in a motorbike or car
• Diesel in a bus, truck or generator
• Kerosene in a wick stove or lamp, and as the base of aviation turbine fuel
• LPG in a domestic cooking cylinder
• CNG in an auto-rickshaw or city bus
• Natural gas piped to a household stove or boiler

Every one of these traces back to coal, crude oil or natural gas.

#How much of world energy they supply

Fossil fuels provide roughly 80% of global primary energy. The share has fallen slowly as renewables have grown, but the absolute quantity consumed has not fallen, because total demand keeps rising.

The reasons for that dominance are practical rather than political:

• High energy density. Petrol carries roughly 12 kWh per kilogram — far more per unit mass than any battery in production.
• Storability. A tank of diesel holds its energy indefinitely with no losses.
• Existing infrastructure. Refineries, pipelines, filling stations, boilers and engines were all built around these fuels over a century.
• Dispatchability. A gas turbine produces power on demand, regardless of weather or time of day.

#The costs

The same combustion that makes them useful causes the problems:

• Carbon dioxide, the principal greenhouse gas driving climate change
• Sulphur dioxide from sulphur-bearing coal and oil, causing acid rain
• Oxides of nitrogen, contributing to smog and acid rain
• Particulates and soot, linked to respiratory and cardiovascular disease
• Carbon monoxide wherever combustion is incomplete
• Ash and slag requiring disposal, and land damage from mining and spills

And underlying all of it, the fact that reserves are finite.

#Fossil fuels versus the alternatives

	Fossil fuels	Renewables
Source	Ancient buried organisms	Sun, wind, water, heat, biomass
Renewable	No	Yes
CO₂ at point of use	High	None or near-zero
Energy density	Very high	Low to moderate
Availability	Depletes	Continuous but variable

#The compact answer

Fossil fuels are fuels formed from the remains of dead plants and animals buried under the earth for millions of years and converted by heat and pressure into carbon-rich substances. The three fossil fuels are coal, petroleum and natural gas. Examples: coal used in power stations, and petroleum, from which petrol, diesel and kerosene are obtained.