Oud comes from the wood of the tropical Agar (Aquilaria) tree, a genus that includes 15 different species.This is the perfume ingredient oud, which is also called agarwood, oudh, agalocha, aloeswood, or eaglewood. Agarwood is a rarity on many fronts. Because the resin is only triggered by the mold, it's estimated that a total of 2 percent of these trees produce it. Not only does this raise the price of the oil, the wood is also one of the most expensive on the market.