A detailed examination has been made on the use of the comparative method for measuring the thermal conductivity of solid materials. Existing data analysis methods are discussed and new techniques, based on generalized linear least squares methods, are presented. An error analysis is made to determine the potential accuracy, reproducibility, and repeatability of the technique. For the case in which the reference conductivity is known to a relative accuracy of +-5%, the overall relative accuracy of the measurement is shown to be about +-6%. Experimental data are presented for the conductivities of commonly used reference materials; Pyrex 7740, Pyroceram 9606, Inconel 718, and Armco iron. Data are also given for two potential reference materials: fused silica and 304 stainless steel.