We analyse the magnetic susceptibility chi as a function of temperature (zero pressure) for the transitions of alpha- beta, beta- gamma and gamma-liquid below and above the transition temperatures for oxygen according to a power-law formula. The observed data are used from the literature, and the values of the critical exponents for the magnetic susceptibility are deduced close to the phase transitions in oxygen. Our exponent values give a logarithmic singularity for the magnetic susceptibility chi in the vicinity of T (c) as in the specific heat at constant magnetic field, C (M). Our exponent values (gamma ae integral 0) are not in agreement with the predictions for the magnetic susceptibility (gamma ae integral 1) of some theoretical models, which undergo essentially a second order transition. Our analysis gives an indication that the alpha- beta transition is a weak first order (less discontinuity in chi), whereas the beta- gamma and gamma-liquid transitions are closer to a first order (more discontinuous behaviour than the alpha- beta transition in oxygen). The effect of the magnetic interactions on the alpha- beta, beta- gamma and gamma-liquid transitions in oxygen is explained.