Abstract: This invention provides an adjustable bracket that can be used to attach auxiliary fuel tanks and other tanks to the bottom of a trailer or vehicle. The adjustable nature of the bracket allows it to be used on a variety of trailers, with different widths. The adjustable bracket comprises two parts with one sliding inside of the other. Each part has several slots that can be lined to create a bracket that is the ideal length to span the distance between the side panels of a trailer or vehicle. The bracket has holes in the bottom through which the bracket can be attached to a mounting retainer or strap that holds the tank in place.