Different methods of calculations of thermal conductivity of gas laser mixtures versus temperature are compared in the paper. Approximation functions describing the experimental data of thermal conductivity and viscosity of the chosen gases (CO/sub 2/, N/sub 2/, He, Xe, CO, O, Ar) are given. The formulas introduced and data obtained allow us to predict thermal conductivity and temperature distribution of a typical high power laser gas mixture. Examples of temperature distribution in RF excited CO/sub 2/, CO, and Xe laser media are shown. Knowledge of the temperature distribution in the laser cavity can be useful for predicting general optical properties of the laser.