Emergency cases for resuscitation include built-in oxygen cylinders with limited oxygen supply. The use of a bag-valve mask device (BVMD) with a reservoir requires a high constant flow of oxygen to maintain a high concentration of delivered oxygen. The goal of the study was to analyze what fraction of inspired oxygen (FiO2) can be reached and how long it takes using different BVMD with their reservoir device and different oxygen flows in order to allow a reduction in oxygen requirements during simulated cardiopulmonary resuscitation (CPR). Experimental analysis was carried out during simulated CPR on the effect in the final FiO2 and the time required to reach it using two different models of BVMD with their reservoir device: Mark IV and Revivator-Plus and four different oxygen flows 5, 10, 15, and 10 l/min during 1 min, followed by 5 l/min (10-5). With both the BVMDs studied, the FiO2 values reached at 10, 15, and 10-5 l/min were higher than 0.85 [Mark IV=0.87 (0.01); Revivator=0.93 (0.03)] in 60 s. At 5 l/min FiO2 were lower in 60 s (P<0.001) and were higher than 0.85 [Mark IV=0.90 (0.005); Revivator=0.90 (0.005)] in 80 s. The mean FiO2 was lower with the Mark IV (P<0.05) (Table 1). To allow a substantial reduction in oxygen requirements, a 10 l/min for 1 min, followed by 5 l/min of oxygen flow can be used during CPR with both BVMDs studied. Increasing supplemental oxygen flow did not appreciably increase the FiO2.