16 CFR 306.11 - Recordkeeping.
You must keep for one year any delivery tickets or letters of certification on which you based your posting of automotive fuel ratings. You also must keep for one year records of any automotive fuel rating determinations you made according to § 306.5. These records may be kept at the retail outlet or at another, reasonably close location. They must be available for inspection by Federal Trade Commission and Environmental Protection Agency staff members or by persons authorized by FTC or EPA.