Mont. Code Ann. § 82-15-103

The standards and specifications for petroleum products, including but not limited to gasoline, ethanol-blended gasoline, fuel oils, diesel fuel, kerosene, and liquefied petroleum gases, must be determined by the department and must be based on nationally recognized standards and specifications such as the standards and specifications that are published by the American society for testing and materials. The standards and specifications adopted by rule by the department are the standards and specifications for products sold in this state, and official tests of the products must be based on the adopted standards and specifications.