An experimental investigation was done on oxygen transfer into a laminar flow of whole blood and saline solutions downstream of an abrupt pipe expansion. This was used as the experimental model for regions of separated flow in the arterial system. The flow was fully-developed prior to the expansion with Reynolds numbers between 160 to 850. The results showed high transfer rates over most of the region downstream of the step, with maximum transfer occurring near the reattachment point. In addition, oscillations of the transfer rate were measured at the larger Reynolds numbers of 450 and 850.