Thermal conductivity measurements were made for the dissociating system 2 NO2 ⇋ 2NO + O2. Experiments were made at temperatures from 548° to 792°K. and pressures from 1 to 30 atm. Under these conditions the chemical reaction is in a nonequilibrium state, and the rate of energy transport is limited by the rates of the forward and reverse reactions. Experimental results agreed very well with a theoretical model based on a linearized reaction rate expression. Using the thermal conductivity results, it was also possible to determine the chemical kinetic constants for the reaction.