Whether the United States Environmental Protection Agency may interpret the ethanol-waiver provision in 42 U.S.C. § 7545(h)(4) to apply to fuel blends whose concentration of ethanol exceeds 10 percent

QUESTION PRESENTED The Clean Air Act prohibits the summertime sale of gasoline whose volatility, measured in Reid Vapor Pressure, exceeds 9 pounds per square inch. 42 U.S.C. § 7545(h)(1). Blending ethanol into gasoline increases the gasoline’s volatility. So, to promote the use of ethanol in gasoline, the Act includes an “[e]thanol waiver” that increases the summertime volatility limit by 1 pound per square inch “{flor fuel blends containing gasoline and 10 percent denatured anhydrous ethanol.” 42 U.S.C. § 7545(h)(4). The question presented is: Whether the United States Environmental Protection Agency may interpret the ethanol-waiver provision in 42 U.S.C. § 7545(h)(4) to apply to fuel blends whose concentration of ethanol exceeds 10 percent. @