When determining extracorporeal oxygen transfer (V_MLO₂) during venovenous extracorporeal membrane oxygenation (VV ECMO) dissolved oxygen is often considered to play a subordinate role due to its poor solubility in blood plasma. This study was designed to assess the impact of dissolved oxygen on systemic oxygenation in patients with acute respiratory distress syndrome (ARDS) on VV ECMO support by differentiating between dissolved and hemoglobin-bound extracorporeal oxygen transfer. We calculated both extracorporeal oxygen transfer based on blood gas analysis using the measuring energy expenditure in extracorporeal lung support patients (MEEP) protocol and measured oxygen uptake by the native lung with indirect calorimetry. Over 20% of V_MLO₂ and over 10% of overall oxygen uptake (VO_{2 total}) were realized as dissolved oxygen. The transfer of dissolved oxygen mainly depended on ECMO blood flow (BF_ML). In patients with severely impaired lung function dissolved oxygen accounted for up to 28% of VO_{2 total}. A clinically relevant amount of oxygen is transferred as physically dissolved fraction, which therefore needs to be considered when determining membrane lung function, manage ECMO settings or guiding the weaning procedure.