An organic solvent based, thermosetting coating composition of a hydroxy functional epoxy-polyester graft copolymer and blocked polyisocyanate crosslinking agent. The coating composition may be formulated as a hot sprayable, high solids coating composition suitable for use as a chip resistant automotive vehicle primer adapted for use on body panel areas subject to chipping by stones, gravel and other road debris. Alternatively, the composition may be formulated as a high solids composition sprayable with conventional spraying equipment. Hydroxy functional epoxy-polyester graft copolymer is prepared by polymerization of lactone monomers in the presence of hydroxy functional epoxy ester resin precursor. Such precursor resin is formed by reaction of diepoxide chain extended substantially simultaneously with diphenol and dicarboxylic acid and chain terminated with acid component comprising primary hydroxy functional acid.