Gas Accessibility and Stabilization Act of 2013 - Amends the Clean Air Act to revise procedures for waiver by the Administrator of the Environmental Protection Agency (EPA) of a control or prohibition regarding the use of a fuel or fuel additive by: (1) allowing waiver if the Administrator determines that extreme and unusual fuel or fuel additive supply circumstances are the result of a problem with distribution or delivery equipment necessary for the transportation or delivery of such fuel or additives, (2) allowing extension of a waiver for more than 20 days if it is determined that the waiver conditions will exist beyond 20 days, and (3) deeming a request for a waiver that is not approved or denied within 3 days to be approved for the period requested.

Amends the Energy Policy Act of 2005 to modify a fuel system requirements harmonization study to: (1) include consideration of biofuels, (2) add consideration of the projected effects of EPA Tier III requirements on air quality and motor fuel prices, and (3) extend to June 1, 2014, the date for submission to Congress of a report on the results of the study.