Ozone yields have been measured from the Febetron irradiation of mixtures containing 1–50 mol% oxygen and each of the five rare gases. The maximum values of G(O3) calculated using the energy absorbed only in the rare gas are obtained with the addition of less than 10% oxygen and are for: He, 16; Ne, 14; Ar, 11; Kr, 10; Xe, 12; each with an uncertainty of less than ±10%. On the addition of 0.2 mol% SF6 these yields are reduced to 6,5,1,2, and 2.5 respectively.These values are compared with those derived from ion and excited state yields and the contributions of subexcitation electrons.