Measurements of oxygen transmissibility are reported for hydrogel lenses of different power. Center thickness is related to oxygen transmissibility, and it is shown that the relation is different for lenses of high dioptric power compared with lenses of low power. For high plus lenses, the oxygen transmissibility is higher than would be expected from a simple consideration of center thickness and the oxygen permeability of the contact lens material. For high minus lenses, the oxygen transmissibility is less than would be expected. Clinically, this means that power as well as center thickness must be taken into account when estimating the oxygen transmissibility of high power lenses.