The oxygen performance of a hydrogel contact lens is arguably its most important property when considering the possible physiological response of the eye. However, information about this aspect of a contact lens can frequently be difficult to obtain, and there are numerous pitfalls in the interpretation and application of the available data. This paper presents the oxygen permeability and oxygen transmissibility of 17 different lens types as measured by one technician in one laboratory across a short time interval. The clear relationship between water content and oxygen permeability is confirmed, and the transmissibilities of three lens types across a wide power range are reported.