The invention relates to antioxidant compositions for lubricants and organic polymers comprising a first antioxidant comprising a reaction product of p-cresol, dicyclopentadiene and isobutylene; and a second antioxidant comprising a diarylamine. The first antioxidant preferably has the structure: wherein n is 0-50, and R1 and R2 are independently hydrogen, a straight or branched C1-C30 alkyl or alkylene group optionally substituted with one or more substituents, C3-C12 cycloalkyl, C5-C12 aryl, or C6-C12 alkylaryl. The second antioxidant preferably has the formula: (R3)a—Ar1—NH—Ar2—(R4)b wherein Ar1 and Ar2 are independently aromatic hydrocarbon groups and R3 and R4 are independently hydrogen or hydrocarbyl groups having from 6 to about 100 carbon atoms and a and b are independently 0 to 3 but (a+b) is not greater than 4.