Continual improvement of oxygenators has been important in the growing demands of patient safety and support during cardiopulmonary bypass. The purpose of this study was to compare the Maxima 1380 oxygenator to the upgraded Maxima Plus oxygenator. Thirty-two adult patients were randomized to either the 1380 group or the Plus group. Information was recorded on the patients' weight, age, body surface area, esophageal temperature, arterial temperature, venous oxygen saturation, arterial pO2, arterial pCO2, blood flow, hematocrit, gas sweep, and FiO2. No significant difference was found between the two groups' mean weight, body surface area, arterial pO2 arterial pCO2, age, esophageal temperature, arterial temperature, venous oxygen saturation, and blood flow (p > 0.05). The Plus group demonstrated significantly lower mean gas sweep rates and FiO2 settings than the 1380 group. FiO2 of the 1380 was dependent on age, body surface area, blood flow, and esophageal temperature (r = 0.89, p < 0.001). FiO2 of the Plus was correlated with weight, esophageal temperature, arterial temperature, and arterial pO2 (r = 0.93, p < 0.001). Gas sweep rate of the 1380 was dependent on age, weight, esophageal temperature, blood flow, arterial temperature, and arterial pCO2 (r = 0.84, p < 0.001). The gas sweep rate of the Plus was dependent on weight and esophageal temperature (r = 0.55, p < 0.001). Based on these analyses, the new Maxima Plus oxygenator is more efficient in oxygen and carbon dioxide transport than the Maxima 1380.