### Question
How is the term ultra-low sulfur diesel fuel defined?


### Answer
The term **ultra-low sulfur diesel fuel** is defined in *42 U.S.C. § 16091a* as the following:

> diesel fuel that contains sulfur at not more than 15 parts per million

#### Citation:
  - *42 U.S.C. § 16091a*
  - Heading: **CHAPTER 149-ENERGY POLICY, 2005 > SUBCHAPTER VII-VEHICLES AND FUELS > Part C-Clean School Buses**

