Little is known about mechanism of action of pre-oxygenated University of Wisconsin solution (UW) over perfluorodecalin (PFD) in enhancing islet yield after cold storage. Therefore, the specific aims of this study were (1) to investigate the dynamic oxygen content changes in gassed preservation solutions (PFD and UW) in the presence of rat pancreas, and (2) to correlate this information with islet yields and morphology after organ storage under these conditions. Methods. Wistar rat pancreata were preserved with either UW solution, pre-gassed UW solution (0.25 L/min of 100% oxygen for 50 min) or pre-gassed TLM solutions for 24 h. During preservation, pO 2 of solutions was measured once per hour with an oxygen meter. After preservation, pancreata were digested for islet isolation via standard techniques, and yields were calculated. Some pancreata in each group underwent formalin fixation and hematoxylin and eosin (H&E) staining. Freshly isolated islets were used as controls. Results are expressed as mean ± SEM; ANOVA was used to compare multiple groups, and P < 0.05 was considered significant. Results. After 24-h preservation, pO2 of PFD in TLM (824.8 ± 40.6 mbar) was not significantly different from pO2 at 0 h (829.2 ± 34.5 mbar, P = NS). While pO2 in UW in TLM (455.6 ± 13.1 mbar) significantly decreased 24 h later (208.5 ± 9.6, P < 0.05), pO2 (161.5 ± 20.5 mbar, P = NS) in the gassed UW alone was not different at 24 h, although these pO 2’s were significantly higher than in ungassed UW (70.0 ± 5.6 mbar). IEQs of “fresh,” “TLM,” and “gassed UW” group (595.7 ± 115, 531.2 ± 72.7, and 497.6 ± 61.0, respectively) were all significantly higher than that of “cold UW” group (288.3 ± 49.8, P < 0.05), without significant differences among these three groups. Microscopically, nuclear pyknosis (apoptotic changes) and karyolysis were more widely observed in pancreata preserved in ungassed UW than in gassed UW and TLM. Conclusions. UW in TLM and pre-oxygenated UW alone result in similar oxygen decay profiles and tissue preservation in the presence of rat pancreas compared with unoxygenated UW alone.