The yield of ozone from the radiolysis of gaseous oxygen has been measured at 1026–1027 eV g−1 s−1 to be G(O3) = 12.8 ± 0.6, in reasonable agreement with the value of 13.8 of Ghormley, Hochanadel, and Boyle (2a). At 1016 eV g−1 s−1, our results and re-examination of previous data give G(O3) = 6.2 ± 0.6. The same value is obtained at the high dose rates by the addition of electron scavengers. The difference in yields on going from high to low dose rates and the decrease with electron scavengers at the high dose rate is explained by differences in ion neutralization processes. These are supported by computer calculations. The mechanism of the neutralization steps is discussed in terms of the applicability of the electron jump theory and the effect of clustering of the ions.The proportion of energy lost to ionization, excitation, and subexcitation electrons is calculated. This is based on the W value, relative cross sections for ionization, and the potential energy curves for O2+ ions. A predicted yield on this basis is G(O3) = 14.0 ± 0.9, in fairly good agreement with the experimental yield.