From a press release issued by the Ministry of Economy in El Salvador:

In Central America, El Salvador is positioned on top for having the lowest prices on regular gasoline, and in second place for the lowest prices on special gasoline and diesel.

AVERAGE PRICES IN CENTRAL AMERICAN GASOLINE AND DIESEL up to 1 March 2013
(Dollars / gallon)

____Country________DIESEL____REGULAR____SPECIAL

EL SALVADOR____4.34________4.26________4.64

GUATEMALA_____4.25________4.40________4.59

HONDURAS______4.37________4.60________4.99

NICARAGUA_____4.69________5.10________5.48

COSTA RICA____4.78________5.06________5.36