The present invention provides for a resin system and coating composition suitable for direct application to metal substrates. The composition may include a phosphate functional polyester. The polyester may be an unsaturated polyester polyol. The coating composition may further include a suitable curing agent, such as an isocyanate or melamine. The composition can be applied through traditional application equipment onto a variety of metal substrates and cures to an acceptable surface for further processing, such as top coating with basecoat and clearcoat.