New polyhydric phenol coesters are disclosed of polyhydric phenols, having 2 to 3 phenolic hydroxyl groups and 1 to 3 benzenoid rings, with carbonic acid and an inorganic acid which can be phosphorous acid, phosphoric acid, and boric acid. The new coesters have molecular weights from 700 to about 10,000, preferably from 1200 to 7000, and are highly effective stabilizers for a variety of synthetic resins.Stabilizer compositions comprising a polyhydric phenol coester and a known polymer stabilizer, as well as synthetic resins stabilized with such stabilizer compositions, are also disclosed.