Fuel is any substance that releases energy, and humans use it for nearly everything: moving vehicles, generating electricity, heating homes, manufacturing materials, and even powering the cells in your body. The vast majority of the world’s fuel consumption falls into four major categories: transportation, industrial production, electricity generation, and residential use. Oil alone accounts for 169 exajoules of global consumption per year, with nearly half of that going to road transport.
Transportation: The Largest Consumer of Oil
Road vehicles burn the biggest share of the world’s oil supply. Cars, trucks, and buses account for 49.2% of all oil consumed globally, making personal and commercial driving the single largest use of fuel on the planet. Aviation takes another 8.6%, mostly in the form of jet kerosene, while shipping and maritime transport consume 6.7%, primarily as heavy fuel oil or marine diesel. Rail is a small slice at just 0.8%, since many rail systems run on electricity instead.
Each mode of transport relies on a slightly different fuel. Gasoline and diesel dominate road travel. Jet fuel (a refined kerosene) powers commercial aircraft. Large cargo ships burn heavy fuel oil, a thick residual product left over after refining crude oil into lighter fuels. Natural gas plays a minor but growing role in transport overall, representing about 7.3% of global natural gas consumption.
Industrial Heat and Manufacturing
Factories and industrial facilities are massive fuel consumers, and much of that fuel goes toward generating extreme heat. About 90% of industrial process heat comes from burning fossil fuels. Natural gas is the dominant choice, making up 55% of industrial fuel use, followed by byproduct fuels at 36% and coal at 4%.
The reason industry needs so much fuel is temperature. Smelting iron requires furnaces reaching roughly 3,000°F. Cement kilns, steel mills, and aluminum smelters all depend on sustained, intense heat that electricity alone has historically struggled to provide at scale. A blast furnace producing iron, for instance, uses coke (a coal product) both as a heat source and as a chemical reactant to strip oxygen from iron ore. Cement production similarly requires burning fuel to heat limestone above 800°C, a process that releases carbon dioxide from both the fuel and the rock itself.
Beyond heat, industry uses fuel as a raw material. About 16.7% of all oil consumed globally goes to “non-energy” uses, meaning the oil isn’t burned at all. Instead, it becomes the feedstock for plastics, synthetic rubber, lubricants, solvents, and thousands of petrochemical products. Natural gas serves a similar dual role: 11.9% of its consumption goes to non-energy applications like fertilizer production, where hydrogen extracted from natural gas is combined with nitrogen to make ammonia.
Electricity Generation
Power plants convert the chemical energy in fuel into electricity by burning it to produce steam, which spins a turbine connected to a generator. Coal, natural gas, and nuclear fuel are the three main sources. Coal dominates in heavy industrial economies, while natural gas has become the preferred fuel for newer power plants because it burns more cleanly and can ramp up and down quickly to match demand.
Nuclear power works differently. Instead of combustion, nuclear plants split atoms of uranium-235. When a neutron strikes a uranium atom, the atom breaks apart, releasing heat and additional neutrons that split more atoms in a chain reaction. That heat boils water into steam, which drives turbines just like in a fossil fuel plant. The uranium fuel must be enriched so that 3% to 5% of it is the fissile uranium-235 isotope, up from less than 1% in natural ore. A single pressurized-water reactor contains 150 to 200 fuel assemblies, and these can generate electricity for years before needing replacement.
Oil’s role in the global energy picture is gradually shrinking. Its share of total energy demand recently fell below 30% for the first time, down from a peak of 46% half a century ago. Renewables now account for the largest share of growth in global energy supply at 38%, followed by natural gas at 28%.
Heating and Cooking in Homes
Residential fuel use varies dramatically depending on where you live. In wealthier countries, natural gas is the primary fuel for home heating and cooking, making up 29.7% of global natural gas consumption. Liquefied petroleum gas (LPG), electricity, and heating oil fill out most of the rest.
In lower-income regions, the picture looks very different. Around 2.1 billion people worldwide still cook using solid fuels like wood, crop waste, charcoal, coal, and animal dung, often in open fires or simple stoves. Over 750 million people lack electricity entirely, forcing them to rely on kerosene lamps for light. The health consequences are severe: incomplete combustion of these fuels causes indoor air pollution that kills an estimated 2.9 million people each year. Rural communities are hit hardest. In 2021, 49% of the global rural population still depended on polluting fuels for cooking, compared to just 14% in urban areas. Sub-Saharan Africa faces the steepest challenge, where 923 million people lacked access to clean cooking fuels as of 2022.
Your Body Runs on Fuel Too
Fuel isn’t just an industrial concept. Your body runs on chemical fuel, primarily glucose, a simple sugar your cells convert into a molecule called ATP that powers virtually every biological process. When glucose enters a cell, it goes through a series of chemical reactions that progressively extract energy. The first stage alone produces a small amount of ATP, but the later stages, which take place inside structures called mitochondria, generate far more. One molecule of glucose ultimately yields dozens of ATP molecules.
When glucose runs low, your body switches to burning fat. Fatty acids are broken down into molecules that feed into the same energy pathways. During prolonged periods without food, your body releases hormones that increase fat burning and reduce the rate at which cells use glucose, preserving what little sugar remains for the brain and other critical organs. Excess glucose gets stored as glycogen in your liver and muscles, essentially a short-term fuel reserve your body can tap between meals.
Hydrogen and Emerging Fuel Applications
Hydrogen already has significant industrial uses. Nearly all hydrogen consumed in the United States goes toward refining petroleum, treating metals, producing fertilizer, and processing foods. Petroleum refineries use it to lower the sulfur content of fuels, and biofuel producers use it to create renewable diesel from vegetable oils.
As a transportation fuel, liquid hydrogen can power fuel cell vehicles or burn directly in truck, rail, marine, and rocket engines. NASA operates the two largest liquid hydrogen storage tanks in the world for its launch vehicles. Several natural gas power plants are also exploring hydrogen as a partial or full replacement for natural gas in electricity generation, which would significantly reduce carbon emissions from the power sector.