An improved method of preparing polyurethane foam by reacting an organic polyisocyanate with a polyol in the presence of water and a combination of a gelling catalyst and a blowing catalyst, in which the blowing catalyst is a compound represented by the following formulae: :M(L.sup.1)(L.sup.2)(L.sup.3)(L.sup.4)!.sub.n :M(L.sup.1)(L.sup.2)(L.sup.3)!.sub.n :M(L.sup.1)(L.sup.2)!.sub.n :M(L.sup.1)!.sub.n wherein M is titanium, zirconium, or hafnium; n ranges from 1 to 20; and each of L.sup.1, L.sup.2, L.sup.3, and L.sup.4 is the same or different ligand selected from the following groups: (1) oxygen, sulfur and nitrogen; (2) an alcoholate, phenolate, glycolate, thiolate, carboxylate, dithiocarbamate, aminate, aminoalcoholate, phosphate, phosphonate, pyrophosphate, sulfonate, or silylamide any of which contains from 1 to 20 carbon atoms and, optionally, contains one or more functional groups, or oxygen, sulfur, nitrogen, or phosphorus-containing; (3) a chelating ligand, such as, various non-fluorine containing and non-sterically hindered .beta.-diketones, triethanolamine, salicylaldehyde, and salicylamide.