Marine Urea Solution 40%, or AUS 40, is an aqueous high-purity urea solution at a concentration of 40% that is needed to operate converters with SCR in applications with large combustion engines. As the name implies, Marine DEF is used in many marine applications but is increasingly used in rail and other land-based applications. Pack Sizes available: 330 Gal Tote - Weight is 3,200 lbs.