An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to www.epa.gov. This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Fuels Registration, Reporting, and Compliance Help

Clarify that the proper version of the Complex Model that is to be used with an augmentation is the version that was in effect at the time the augmentation was approved. The preamble and regulations are inconsistent on this issue, and confusion arises in