X-ray photoelectron spectroscopy (XPS), tensiometric wetting, and atomic force microscopy (AFM) were used to investigate the surfaces of PAN based carbon fibers. Percent weighted dipole moments (%WDM) were computed from the deconvoluted core level carbon XPS peaks. Tensiometric wetting separated the polar and dispersive components of the fiber surface energies thus allowing the computation of % polar energies. AFM provided quantitative measurements of the fiber surface rugosities. Scanning electron microscopy (SEM) revealed adhesive interfacial fractures for PMR-15 (polyimide) composites of fibers with low %WDM and % polar energies; cohesive fractures for those with high %WDM and % polar energies. Increasing interlaminar shear strengths correlated with increasing %WDM and % polar energies. The fibers with higher %WDM also had rougher surfaces which probably expose more graphite basal plane dipole sites in addition to providing mechanical interlocking.