Succinate-based plasticizer mixtures have potential use as nontoxic and sustainable plasticizers and as replacements for commonly used phthalate plasticizers. Synergistic effects occur when the interaction between two materials is enhanced by the addition of a third component. This concept was applied to plasticizers within a polymer matrix. Three newly synthesized succinate-based plasticizers (di-ethylhexyl succinate, di-decyl succinate, and di-dodecyl succinate) were tested for their plasticizing ability. Then, di-decyl succinate and didodecyl succinate were blended with the previously reported succinate di-esters (di-ethyl succinate, di-hexyl succinate, and di-octyl succinate) to study their plasticizing efficiency. Mixtures of these higher molecular weight (MW) succinate di-esters and previously reported lower MW ones were found to be more effective at plasticizing poly(vinyl chloride) compared to the individual succinate plasticizers alone.