This action makes corrections and updates to source test methods, performance specifications, and testing regulations for air emission sources under 40 CFR parts 51, 60, and 63. The revisions include corrections to testing provisions that contain inaccuracies and typographical errors, updates to outdated test methods, and the addition of alternative testing procedures the Agency has deemed acceptable to use. An example correction is in Method 204, where the current enclosure area ratio, which is inadvertently identified as being less than 10.05, is being revised to be less than 0.05. This action is developed every few years to keep rules up to date and to ensure that compliance testing and monitoring are done correctly.