On February 28 and 29, 2012, the U.S. Court of Appeals for the District of Columbia Circuit heard oral argument challenging rulemakings issued by the U.S. Environmental Protection Agency (EPA) to regulate greenhouse gas (GHG) emissions from automobiles and manufacturing facilities under the Clean Air Act. The court's decision will address the proper scope of EPA’s prevention of significant deterioration (PSD) program and of rarely invoked judicial doctrines of last resort like “absurd results” and “administrative necessity” in the context of GHG emissions. In this article, the authors argue that EPA need not and should not have turned to doctrines of last resort to justify rewriting the Act’s major source thresholds, and instead should have implemented statutory language that by its terms limited applicability of the PSD permit program (the "situs requirement"). The article explains the situs argument under the Clean Air Act and how its adoption would implement “statutorily compelled tailoring” rather than a tailoring approach that abrogates to EPA the authority to determine which plants are subject to PSD and which are not. It also outlines the opportunities that EPA had to avoid the “absurdities” and “administrative necessities” it claimed required it to revise plainly written statutory thresholds as it was moving toward issuing the Tailpipe Rule in 2009 and 2010. Finally, the article explains the practical implications of implementing situs as was originally dictated by statutory language, contemplated by the Congress, and required by the Alabama Power Co. v. Costle decision.