To test the hypothesis that a fractional inspired oxygen (F I O 2 ) of 1.0 compared to 0.4 during hemorrhagic shock (HS) and fluid resuscitation (FR): mitigates tissue dysoxia; however, enhances the oxidative stress; therefore, offsets the benefit on survival.Thirty rats underwent: HS for 75min, during which 3.0mL/100g of blood was withdrawn, followed by FR for 75min, during which 1.0mL/100g of shed blood and 3.0mL/100g of crystalloid solution were infused. Ten rats were randomized into one of three F I O 2 (0.21 vs. 0.4 vs. 1.0) groups, and observed for survival until 72h in each group. Hemodynamics, liver tissue PO 2 (P T O 2 ), and, plasma antioxidants levels were also monitored.Oxygen inhalation increased mean arterial pressure (MAP) and decreased heart rate (HR) during HS and FR. Liver P T O 2 was less than 10Torr in all groups throughout HS; while it increased to average 26–35Torr in oxygen groups during FR, it remained at 10Torr with F I O 2 0.21 (P<0.01). MAP, HR, and P T O 2 did not differ significantly between oxygen groups. Plasma antioxidants levels did not differ among the three groups. All rats treated with oxygen, but eight of 10 rats with F I O 2 0.21 survived up to 72h (NS).Supplemental oxygen does not mitigate tissue dysoxia during HS, but does reduce tissue dysoxia without enhancing oxidative stress during subsequent FR. Increased F I O 2 appears to prolong survival. These beneficial effects of supplemental oxygen do not differ between an F I O 2 of 0.4 and 1.0.