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   Yellow grease is derived from used cooking oil from the fast-food industry. It is used to feed livestock, and to make soap, make-up, clothes, rubber, detergents, and biodiesel fuel.[1]

It is distinct from brown grease; yellow grease is typically used-frying oils from deep fryers, whereas brown grease is sourced from grease interceptors.[2]. Yellow grease can also refer to lower-quality grades of tallow (cow or sheep fat) from animal rendering plants.

Yellow grease is traded as a marginally valuable commodity, and has traditionally been used to spray on roads as dust control, or as animal feed additive, but has become a feedstock for biodiesel production. Although most biodiesel is produced from renewable plant sources, yellow grease is attractive because it is inexpensive and its use converts waste into fuel.

http://en.wikipedia.org/wiki/Yellow_grease