Several mathematical models for the bidirectional reflectivity distribution function (BRDF) are compared to plane-of-incidence (PLIN), BRDF measurements of opaque surfaces. A laser at 0.6328 micrometers wavelength was the source for the BRDF measurement instrument; the theoretical measurement accuracy was to within 2%. Data are given for a glossy white paint, a glossy black paint, and a mill finished aluminum. The goal was to find a BRDF model that can represent the measured data to within 10% for any incident/reflected angle. Neither the Lambertian, Phong, Harvey, nor Cook-Torrance models had the desired accuracy for the three samples. A method which is based on interpolation and extrapolation of the empirical data is proposed which may achieve the desired goal both in and out of the PLIN.