The U.S. Environmental Protection Agency requires high-sulfur diesel to contain a red dying agent, and it is illegal to tamper with diesel to remove the dye, as of 2015. The Internal Revenue Service also mandates that tax-exempt diesel contains a red dye to distinguish it from taxable fuels and prevent individuals from using it to dilute clear diesel fuel.
Red-dyed diesel fuel is typically used in off-road applications, such as to provide fuel for heating and operating farm and construction equipment. In most cases, it is illegal to operate a motor vehicle on public roads in the United States with dyed diesel fuel.
Because it is not subject to the same taxes as diesel for transportation use, red-dyed diesel is typically less expensive than other commercial diesel fuels, but drivers illegally using the fuel or trying to alter or remove the dye are subject to civil and criminal penalties. Depending on the jurisdiction and number of infractions, violators may receive fines and other civil penalties and criminal charges, including jail time.
Solvent 26, a fuel-solvent liquid, is the standard dye manufacturers use in the United States for this purpose, though the more soluble Solvent Red 164 is increasingly replacing it in commercial use. The dye has no material effect on the performance of the fuel, and manufacturers only apply it for identification and legal compliance purposes.