Oil Spring is an oil seep located approximately 6 miles north of Ca?on City, Colorado. The purpose of this study is to determine whether the oil from Oil Spring and the oil from nearby Florence oil field share a common source. Bulk and molecular geochemical analyses show that the oil seep is most likely derived from a group of geochemically similar Cretaceous source rocks including the Carlile Shale, Greenhorn Limestone, Graneros Shale, and the Mowry Shale. The Florence oil is derived from the Sharon Springs Member of the Upper Cretaceous Pierre Shale.