The extended retardation of the free-radical seeded emulsion polymerisation of vinyl acetate by oxygen has been modelled and fitted to experimental data. It is argued that the unusually long retardation observed in this system is due to the high entry efficiency of the aqueous-phase oligomeric radicals which allows latex particles to compete with dissolved oxygen for these initiating radicals. This, in the case of VAc, is due to the high value of the product of the propagation rate coefficient and the water solubility. As oxygen is consumed the competition increasingly favours entry of initiating radicals into particles and the polymerisation rate gradually increases. The model also qualitatively predicts the much shorter retardation behaviour of styrene and MMA which is due to the lower values of the product of the propagation rate coefficient and the water solubility for these monomers.