40 CFR 80.1125 - Renewable Identification Numbers (RINs).
Each RIN is a 38 character numeric code of the following form:
(a) K is a number identifying the type of RIN as follows:
(e) BBBBB is a serial number assigned to the batch which is chosen by the producer or importer of the batch such that no two batches have the same value in a given calendar year.
(g) D is a number identifying the type of renewable fuel, as follows:
(i) EEEEEEEE is a number representing the last gallon-RIN associated with a batch of renewable fuel. EEEEEEEE will be identical to SSSSSSSS if the batch-RIN represents a single gallon-RIN. Assign the value of EEEEEEEE as described in § 80.1126.