### Question
What does primary fuel mean?


### Answer
**Primary fuel** has the following meaning in *42 U.S.C. § 7511a*:

> the fuel which is used 90 percent or more of the operating time

#### Citation:
  - *42 U.S.C. § 7511a*
  - Heading: **CHAPTER 83-ENERGY EXTENSION SERVICE > SUBCHAPTER I-PROGRAMS AND ACTIVITIES > Part D-Plan Requirements for Nonattainment Areas > subpart 2-additional provisions for ozone nonattainment areas**

