This study was designed to evaluate the production of cerebral edema [as measured by tissue specific gravity (SpG)] following moderate fluid percussion (FP) and cortical impact (CI) injury in rodents. To determine the effects of a secondary systemic insult, hypoxia (13% oxygen for 30 min) was added to some experimental groups immediately after head injury. To determine the effects of hyperbaric oxygen (HBO) on injured cortical tissue, additional animal groups were exposed to HBO (1.5 atm, for 60 min), beginning 4 h after head trauma. Both injury models produced equal amounts of tissue edema at the site of injury (mean SpG ± SEM = 1.035 ± 0.001), when measured 6 h posttrauma. There was no significant edema at the tissue sites immediately adjacent to the trauma sites. The addition of hypoxia to either injury system did not increase edema formation beyond that produced by injury alone. HBO reduced the water content of the trauma site in animals that had received FP, but not in animals receiving CI. We conclude that with the injury parameters used in this protocol, both FP and CI appear to produce focal cerebral edema at the site of trauma. Hypoxia does not worsen edema. HBO appears to reduce edema produced by FP, but not by CI.