The Capiox RX25 and Quadrox‐i Adult oxygenators are commonly used in clinical adult cardiopulmonary bypass circuits. This study was designed to test the effectiveness of two adult oxygenators in order to evaluate gaseous microemboli (GME) trapping capability and hemodynamic performance. A simulated adult CPB circuit was used and primed with Ringer’s lactate and packed red blood cells (hematocrit 25%). All trials were conducted at flow rates of 2–5 L/min (1 L/min increments) with a closed and open arterial filter purge line at 35°C. The postcannula pressure was maintained at 100 mm Hg. After a 5 cc of bolus air was introduced into the venous line, an Emboli Detection and Classification system was used to detect and classify GME at the preoxygenator, postoxygenator, and precannula sites. At the same time, real‐time pressure and flow data were recorded, and hemodynamic energy was calculated using a custom‐made data acquisition system and Labview software. Our results showed that the oxygenator pressure drops of Quadrox‐i Adult oxygenator were lower than Capiox RX25 at all flow rates. The Quadrox‐i Adult oxygenator retained more hemodynamic energy across the oxygenator. Both oxygenators could trap the majority of GME, but Capiox RX25 did better than the Quadrox‐i Adult oxygenator. No GME was delivered to the pseudo patient at all flow rates in the Capiox group. The Capiox RX25 venous reservoir could capture more GME at lower flow rates, while the Quadrox‐i Adult venous reservoir performed better at higher flow rates. An open arterial filter purge line reduced GME slightly in the Capiox group, but GME increased in the Quadrox group. The Quadrox‐i Adult oxygenator is a low‐resistance, high‐compliance oxygenator. The GME handling ability of Capiox RX25 performed well under our clinical setting. Further optimized design for the venous/cardiotomy reservoir is needed.