The basic unit of compliance in the RFS program is the gallon-RIN. However, for shorthand we allow multiple sequential gallon-RINs to be represented by a single batch-RIN through the appropriate designation of the start (SSSSSSSS) and end (EEEEEEEE) codes in the RIN.
As physical volumes of renewable fuel are split or merged, the assigned batch-RINs can likewise be split or merged in various ways, with the primary restriction being that no more than 2.5 assigned RINs can be transferred with every physical gallon of renewable fuel (see regulation Section 80.1128(a)(4)). See also question 3.7.
Question and Answer was originally posted at: Questions and Answers on the Renewable Fuel Standard Program (PDF) (55 pp, 221 K, EPA420-F-07-041a, August 2007, About PDF)