Predictions of the glass-forming ability and the glass composition range of transition metal alloys are made using a semiempirical theory. The treatment is based on comparing the Gibbs free energies of the competing crystalline and amorphous phases, which requires knowledge of the differences in Gibbs free energy between the amorphous and crystalline phases of the pure elements, Delta G^a-c. In some cases, this quantity can be determined from the available experimental information on glass formation, rather than by using a particular model for Delta G^a-c. The results of the authors' calculations are compared with reported data on systems treated by rapid quenching, mechanical alloying and ion mixing techniques.