Gas Type by Car: Regular, Premium, Diesel or E85 / Mercury / MountaineerMercury Mountaineer Gas type by year YearGas type2010Regular2009Regular2008Regular2007Regular2006Regular2005Regular (flex-fuel E85 engine available)2004Regular (flex-fuel E85 engine available)2003Regular (flex-fuel E85 engine available)2002Regular (flex-fuel E85 engine available)2001Regular2000Regular Source: U.S. EPA / DOE fuel economy data (fueleconomy.gov).