On Tuesday, August 18, 2015, with much fanfare, EPA released pre-publication versions of several proposed rules affecting air quality permitting and regulation of sources in the oil and gas sector. While EPA's promised "methane rules" and proposed Control Technique Guidelines (CTG's) for state emissions control requirements for oil and gas sources may have grabbed the spotlight for being completely new and different among the proposals released, also included was EPA's proposed rule for making Clean Air Act (CAA) source determinations in the onshore oil and gas sector. This proposed Source Determination Rule follows two significant EPA attempts to clarify the process for making source determinations in the onshore oil and gas sector through guidance, but which guidance has not prevented significant litigation and disputes between permitting authorities, the regulated community, and other stakeholders regarding when and how to "aggregate" multiple pollutant emitting activities in the same CAA stationary source permit. Will this third attempt by EPA through rulemaking to clarify the process for making source determinations for oil and gas activities prove successful? We highlight a few significant aspects of the proposed rule below, to help you answer this question for yourself, or develop your own comments.