Ethyl fluid, also known as lead water, is a gasoline antiknock additive formulated from tetraethyl lead, organic halides, and oil-soluble dyes. It is an oily liquid with a distinctive odor and is miscible with gasoline. The organic halides used include ethyl chloride, vinyl chloride, 1-chlorobenzene, dichloroethane, and monofluoroethane, which can convert the lead and lead oxide formed after the combustion of tetraethyl lead into volatile lead halides that are discharged from the cylinder, preventing them from depositing in the cylinder and causing accidents. In addition, the organic halides also stabilize tetraethyl lead. The dyes used usually dye the ethyl fluid bright red, blue, or orange to attract the user's attention and prevent tetraethyl lead poisoning. Currently, the use of leaded gasoline has been gradually prohibited.


Tetraethyl lead was once widely used as an additive in gasoline to increase the octane rating of the fuel, thereby preventing knock in engines and allowing for the use of higher compression ratios, which in turn improved the efficiency and power of automobile engines. In the United States, where tetraethyl lead additives were used, compared to Europe where alcohol was used as an additive, the advantages of leaded gasoline were evident from its high energy content and superior storage quality, making it a widely used fuel additive. One of the major advantages of tetraethyl lead is that it requires very low concentrations to achieve an increase in fuel octane rating compared to other antiknock agents or gasoline blends with higher octane ratings. A typical preparation method involves adding one part of ethyl fluid (containing tetraethyl lead) to 1260 parts of untreated gasoline. Other antiknock agents must be used in larger quantities and/or have lower energy values than natural gasoline. Leaded gasoline with high energy value offers greater fuel efficiency.