['This study evaluated the morphology of the rat liver when hyperbaric oxygen (HBO) was used at various stages of ischemia and reperfusion.', 'Thirty-two male Wistar rats, subjected to 30 minutes of hepatic ischemia and 30 minutes of reperfusion, were randomly assigned as follows: GIR (n\xa0= 8), control without HBO; GHBO/I (n\xa0= 8), in which HBO was applied only during ischemia; GHBO/R (n\xa0=\xa08), HBO only during reperfusion; and GHBO/IR (n\xa0= 8), HBO during both ischemia and reperfusion. Feasibility scores of hepatocytes were determined by assessing 8 items related to liver injury.', 'The histologic injury score of the hepatic specimens was significantly lower in the GHBO/I group (79.0 ± 0.1) compared with the GIR group (135.0 ± 0.1). HBO was not effective when applied during reperfusion (GHBO/R, 151.3 ± 0.1) or during the ischemia plus reperfusion period (GHBO/IR, 131.0 ± 0.1). The sum was significantly higher (P\xa0<\xa0.05) in HBO-treated animals during the reperfusion period (ie, in the GHBO/R group compared with any of the other groups).'] Does period of Hyperbaric Oxygen Delivery lead to Different Degrees of Hepatic Ischemia/Reperfusion Injury in Rats?