Section 1090.305 - ULSD standards(a)Overview. Except as specified in § 1090.300(a) , diesel fuel must meet the ULSD per-gallon standards of this section.(b)Sulfur standard. Maximum sulfur content of 15 ppm.(c)Cetane index or aromatic content. Diesel fuel must meet one of the following standards:(1) Minimum cetane index of 40.(2) Maximum aromatic content of 35 volume percent.