Abstract: Tertiary-butylphenyl diphenyl phosphate esters in which the nominal molar ratio of tertiary-butyl radicals to phenyl radicals ranges from about 1:5 to about 1:2, the meta-tertiary-butylphenyl content ranges from about 25% to about 100 % and the ortho-tertiary-butylphenyl content is less than about 50% are highly effective plasticizers for vinyl chloride polymer compositions.