Gasoline additives are substances added to gasoline to improve its performance and reduce emissions. ETHANOL (7 letters) is an alcohol-based fuel additive that increases octane levels and reduces emissions. ODOR (4 letters) is an additive used to mask the smell of gasoline. Toluene (7 letters) is a hydrocarbon-based fuel additive that increases octane levels and helps prevent engine knocking. STP (3 letters) is a brand of fuel additive that helps clean and lubricate engine parts. Ethyl (5 letters) is an additive used to increase octane levels in gasoline. All of these additives are used to improve the performance of gasoline and reduce emissions.