Fuel additives are chemical substances that are added to gasoline, diesel, kerosene and other fuels to impart or improve certain properties. There are many different types of products. Common types of fuel additives include acetone, ether, nitrous oxide (nitrous), nitromethane (nitro), butyl rubber, ferox, oxyhydrogen, ferrous picrate, silicone and other anti-foaming agents, and tetranitromethane. Gasoline treatments, fuel injector cleaners, fuel injector treatments, octane boosters, diesel fuel treatments, and water removers are also available. Additional categories of fuel additives include antioxidants, hybrid compound blends, oxygenates, antiknock agents, leader scavengers, fuel dyes, metal deactivators, and corrosion inhibitors. Oil additives and fluid additives are related products.

Selecting fuel additives requires an understanding of product capabilities. Ether and other flammable hydrocarbons are used as starting fluids in hard-to-start diesel engines. Both nitrous oxide (nitrous) and nitromethane (nitro) are used in auto racing and other high-performance applications. Acetone is a vaporization additive used mainly with methane racing fuel. Butyl rubber is a detergent for diesel fuel injectors while ferox is an engine catalyst that improves fuel economy and reduces emissions in gasoline engines. Ferrous picrate and oxyhydrogen are also used to improve fuel mileage. Silicone is used as anti-foaming agent in diesel engines. Fuel additives such as tetranitromethane can help to improve the combustion properties of diesel fuel.

Gasoline additives include hybrid compound blends, oxygenates, antioxidants, antiknock agents, lead scavengers and fuel dyes. Hybrid compound blend fuel additives are listed as catalysts, burn-rate modifiers, stabilizers, detergents, dispersants, and corrosion inhibitors. Oxygenates are divided into alcohols and ethers. Methanol (MeOH), ethanol (EtOH), isopropyl alcohol (IPA), n-butanol (BuOH), and gasoline-grade t-butanol (GTBA) are alcohol oxygenates. Ether oxygenates include methyl tert-butyl ether (MTBE), tertiary amyl methyl ether (TAME), tertiary hexyl methyl ether (THEME), ethyl tertiary butyl ether (ETBE), tertiary amyl ethyl ether (TAEE), and diisopropyl ether (DIPE). Specialty gasoline additives are also available.

Antiknock agents, lead scavengers, and fuel dyes are available from suppliers of fuel additives. Tertra-ethyl lead, ferrocene, iron pentacarbonyl, toluene, and isooctane are types of antiknock agents. There are three main types of lead scavengers for leaded gasoline: tricresyl phosphate (TCP), 1,2-Dibromoethane, and 1,2 Dichloroethane. The most common fuel dyes are solvent red 24, solvent red 26, solvent yellow 124, and solvent blue 35. Proprietary fuel additives are also available.