Abstract: Cyclic phosphite structure-containing polyalkyl hindered phenol tetramers are disclosed as novel compounds useful to impart to lubricant oils oxidation and corrosion inhibition. A novel preparative method for the cyclic phosphite-containing polyalkyl hindered phenol tetramers is also disclosed wherein at least a molar excess of a tri(C.sub.1 to C.sub.4 alkyl) phosphite is reacted in the presence of iodine as catalyst with a polyalkyl hindered phenol tetramer of the formula: ##STR1## wherein the sum of the carbon atoms in all the R.sub.1, R.sub.2, and R.sub.3 groups is at least 42 and wherein R.sub.1 and R.sub.2 can be C.sub.1 to C.sub.12 alkylhydrocarbon groups and the R.sub.3 groups can each have as many as 200 carbon atoms. The trialkyl phosphite reacts with a pair of adjacent hydroxyl groups to split out 2 molecules of alkanol and form the cyclic phosphite structure: ##STR2## within said tetramer structure. Said R.sub.4 group is the C.sub.1 to C.sub.4 alkyl from the trialkyl phosphite.