What Are Fossil Fuels? (Types, Uses & Impact)

What are fossil fuels?

Fossil fuels are natural energy sources made from the remains of plants and animals that lived millions of years ago. The most common fossil fuels are coal, oil (petroleum), and natural gas. They are rich in carbon and hydrogen and release energy when burned.

How do fossil fuels form?

Fossil fuels form when dead plants and tiny sea creatures are buried under layers of mud and rock. Over millions of years, heat and pressure change that buried material into fuel.

1. Plants and animals die and sink into mud and sediment.
2. Layers build up and pressure rises.
3. Heat and pressure slowly turn the material into coal, oil, or gas.

For a visual explanation of this long process see the Smithsonian summary on how fossil fuels form and the Stanford overview on fossil fuel formation.

Three main types of fossil fuels

Here are the three main types and what makes each one different.

Type	How it forms	Main uses	Quick downside
Coal	From ancient plants in swamps; heat and pressure turn plant material into coal.	Electricity generation, steel production, industry.	High CO2 when burned and air pollution.
Oil (Petroleum)	From tiny sea plants and animals turned into liquid hydrocarbons deep underground.	Fuel for cars, trucks, jets; making plastics and chemicals.	Spills and greenhouse gases.
Natural gas	Often forms with oil or from organic matter that became methane gas.	Heating, electricity, cooking, some industry processes.	Methane leaks are a powerful greenhouse gas.

Trusted sources like Britannica and the EIA glossary list these same main types.

What are fossil fuels used for?

Fossil fuel energy powers much of modern life. Typical uses include:

• Electricity: Burning coal, gas, or oil to make steam that runs turbines.
• Transport: Gasoline, diesel, and jet fuel come from oil.
• Heating and cooking: Natural gas and heating oil warm homes.
• Industry and products: Fossil fuels make steel, cement, plastics, and chemicals.

According to Our World in Data, about 80% of the world's energy still comes from fossil fuels. That shows how central they are to daily life and the global economy.

Why are fossil fuels a problem?

Burning fossil fuels releases carbon dioxide (CO2) and other pollutants into the air. CO2 is a greenhouse gas that traps heat and drives climate change. Other harms include air pollution, oil spills, and habitat destruction from mining and drilling.

Quick data point: fossil fuels are responsible for the majority of human-made greenhouse gas emissions. For more on emissions and impacts, see the Eurostat definition and the U.S. Department of Energy overview.

Practical implication: because these fuels release so much CO2, switching to cleaner energy sources and using less energy are the most direct ways to cut emissions and slow climate change. That means using renewable electricity, improving home insulation, and choosing efficient transport.

Pros and cons at a glance

• Pros: High energy density, reliable power, existing infrastructure, supports many products.
• Cons: Non-renewable (takes millions of years to form), major source of CO2 and air pollution, extraction can harm land and water.

Quick facts

• Fossil fuels formed over millions of years from dead plants and animals (Smithsonian).
• Common fuels: coal, oil, natural gas (EIA).
• They supply about 80% of global energy today (Our World in Data).

Simple FAQ

Are fossil fuels renewable?

No. They are non-renewable because they take millions of years to form. Once used, they cannot be quickly replaced.

How fast do they form?

It takes millions of years. Conditions of pressure, heat, and the type of organic material determine whether coal, oil, or gas forms.

Can we stop using fossil fuels?

Yes, but it takes time. Replacing fossil fuel energy with renewables, improving energy efficiency, and changing how we travel and make goods are key steps. For more context on the global shift, read Our World in Data and the National Geographic explainer.

Where to learn more

Reliable sources: Smithsonian Ocean, Stanford Understand Energy, EIA, Our World in Data, and U.S. Department of Energy. An accessible article for general readers is available from National Geographic.

Infographic and table

Use the downloadable infographic to show how fossil fuels form and the comparison table above when teaching or studying. Example image:

Bottom line: Fossil fuels are powerful and useful, but they are finite and cause pollution and climate change when burned. Learning how they form, where they are used, and their impacts helps people make better choices at school, home, and work.