an ultra high ortho nonyl phenol phosphite is provided in the form of a mixed ortho - para tris nonyl phenyl phosphite composition . the composition is produced by reacting pcl 3 with a nonyl phenyl composition comprising para - unsubstituted / ortho substituted nonyl phenol present at a level of from 98 to 99 . 95 percent by weight based on the total weight of the nonyl phenol composition . the phosphite composition surprisingly and unexpectedly exhibits a substantial increase hydrolyric stability over that of conventional high ortho tris nonyl phenyl phosphite . the phosphite is useful for stabilizing thermoplastic compositions , which may be then extruded or molded into articles such as film , sheet or useful thermoplastic objects .