This action finalizes several specific changes to existing regulations which require the registration and testing of designated motor vehicle fuels and fuel additives (F/FAs) by their manufacturers. Included are changes to the regulatory definitions of ``fuel manufacturer,'' ``additive,'' and ``small business,'' as well as modifications to grouping rules for biodiesel and synthetic fuels. These changes will streamline F/FA registration and testing burdens and reduce the number of respondents, while maintaining the informational value of the program and its contributions to the public health and environmental goals of the Clean Air Act. Another previously proposed change, to establish a de minimis provision for F/FAs containing certain ``atypical'' elements, is not addressed in this action. However, in a direct final rule also published elsewhere in this issue of the Federal Register, certain deadlines related to testing of atypical F/FAs are extended while EPA determines the most appropriate disposition of the de minimis proposal.