An acronym standing for Ammonium Nitrate / Fuel Oil. It is typically used to refer to a type of explosive compound or device made with these base components. The explosives used in the Oklahoma City bombing were ANFO; the components are typically aquired as fertilizer (ammonium nitrate) and diesel fuel (fuel oil). Because these are fairly easy to come by, this combination is popular with terrorists and other illegal users of explosives. The disadvantage to this variant of explosive is that it is relatively weak in terms of energy released per unit mass of substance. As a result, large quantities are required to do severe damage; therefore, bombs made with ANFO are usually delivered inside a vehicle such as a truck (Oklahoma City, World Trade Center) or car. ANFO produces an extreme odor, moreover, which makes producing and transporting it without detection slightly more complicated (although of course by no means impossible).