This investigation explored the influence of supplemental oxygen administered during the recovery periods of an interval-based running session on the post-exercise markers of reactive oxygen species (ROS) and inflammation. Ten well-trained male endurance athletes completed two sessions of 10 × 3 min running intervals at 85 % of the maximal oxygen consumption velocity (vVO(2)peak) on a motorised treadmill. A 90-s recovery period was given between each interval, during which time the participants were administered either a hyperoxic (HYP) (Fraction of Inspired Oxygen (FIO2) 99.5 %) or normoxic (NORM) (FIO2 21 %) gas, in a randomized, single-blind fashion. Pulse oximetry (SpO(2)), heart rate (HR), blood lactate (BLa), perceived exertion (RPE), and perceived recovery (TQRper) were recorded during each trial. Venous blood samples were taken pre-exercise, post-exercise and 1 h post-exercise to measure Interleukin-6 (IL-6) and Isoprostanes (F2-IsoP). The S(p)O(2) was significantly lower than baseline following all interval repetitions in both experimental trials (p < 0.05). The S(p)O(2) recovery time was significantly quicker in the HYP when compared to the NORM (p < 0.05), with a trend for improved perceptual recovery. The IL-6 and F2-IsoP were significantly elevated immediately post-exercise, but had significantly decreased by 1 h post-exercise in both trials (p < 0.05). There were no differences in IL-6 or F2-IsoP levels between trials. Supplemental oxygen provided during the recovery periods of interval based exercise improves the recovery time of SPO(2) but has no effect on post-exercise ROS or inflammatory responses.