The inverted susceptibility is used as a figure of merit to discuss the maser properties of Cr-TiO2atL-band frequencies. This material has the advantage of a high inversion ratio and narrow linewidth resulting in a gain per unit length 10 to 25 times larger than for ruby in the liquid helium temperature range. The optimum concentration of Cr3+is found to be around 0. 016 percent from measured data at 1.4 Gc/s. The gain calculated from the figure of merit agrees with measurements on an actual 1.4 Gc/s traveling-wave maser. The decrease in inversion ratio with increasing Cr3+concentration is an important factor which determines the behavior of the figure of merit. This variation is shown to be consistent with calculations based on a simplified spin-lattice relaxation model.