We evaluated the accuracy of delivery of one type of infusion pump at three nominal flow rates under two environmental pressures (measured in atmospheres absolute, ATA), one of which is used for hyperbaric oxygenation. Overall, we observed significant differences between the two different pressures (1 ATA and 2 ATA). Changes in the rate of delivery of between about -4% and +2% were observed over the time course of hyperbaric oxygenation, and the inter-group difference was significant in the phases in which pressure was changing. The effect produced by 2 ATA was statistically significant but small, and its influence is likely to be negligible during practical hyperbaric oxygenation therapy. Thus, it would seem that this type of pump would deliver reliably at the nominal rate during hyperbaric oxygenation at these levels.