The thermodynamics of the gas-phase 02 dimerization have been computed in terms of partition functions, supplied with parameters from quantum-chemical ab initio computations. Two different evaluations of the dimerization energetics have been employed and three different isomers of the dimer considered. In both sets the non-linear structures co-exist at temperatures relevant for atmospheric conditions. Enhancement of heat capacity through this isomeric interplay is quite large at very low temperatures. For the total dimerization equilibrium constant an interval, in which the true value should be present, is suggested.