Conforms to specifications as established by the American Society for Testing and Materials (ASTM) in the 1980 Annual Book of ASTM Standards, Part 23, page 229, Standard No. D 439-79. Any of the ``seasonal and geographical'' volatility classes for unleaded gasoline are considered suitable as a denaturant. (For incorporation by reference, see Sec. 21.6(b).) [T.D. ATF-133, 48 FR 24673, June 2, 1983. Redesignated by T.D. ATF-442, 66 FR 12854, Mar. 1, 2001]