The Environmental Protection Agency created a tradable commodity called RINs (Renewable Identification Numbers)—serial numbers that allow tracking batches of biofuels—to enforce biofuel mandates. To prove they have met their annual biofuel obligations under the Renewable Fuels Standard gasoline and diesel producers and importers accumulate RINs, by either buying biofuels with attached RINs or by buying detached RINs offered in the RIN market. RINs become detached when biofuels are blended with diesel or gasoline. Blenders who are not obligated parties have no use for their RINs; thus they are willing sellers in the RIN market. The price at which RINs are bought and sold is measured in cents per gallon of ethanol. In 2013, RIN prices have varied dramatically, from less than 10 cents per gallon in January to over 140 cents per gallon in July. As of late October, RIN prices for corn ethanol are about 25 cents per gallon.