Renal oxygen consumption (VO_2,ren) is an important parameter which has been shown to be influenced by various pathophysiological circumstances. VO_2,ren has to be repeatedly measured during an experiment to gain insight in the dynamics of (dys)regulation of oxygen metabolism. In small animals, the classical approach of blood gas analysis of arterial and venous blood samples is only limitedly applicable due to fragile vessels and a low circulating blood volume. We present a phosphorescence lifetime technique which allows near-continuous measurement of renal venous PO₂ (vPO₂) and kidney oxygen consumption (VO₂) in rats. The technique does not rely on penetration of the blood vessel, but uses a small reflection probe, placed in close proximity of the renal vein, for detection of the oxygen-dependent phosphorescence of the injected water-soluble near-infrared phosphor Oxyphor G2. The technique was calibrated in vitro and the calibration constants were validated in vivo in anesthetized and mechanically ventilated male Wistar rats. The hemoglobin saturation curve and its pH-dependency were determined for calculation of renal venous oxygen content. The phosphorescence technique was in good agreement with blood gas analysis of renal venous blood samples, for both PO₂ and hemoglobin saturation. To demonstrate its feasibility in practice, the technique was used in four rats during endotoxin infusion (10 mg*kg^-1*h^-1 during 1 hour). Renal vPO₂ reduced by 40% upon reduction in oxygen delivery to 30% of baseline, but VO₂ remained unchanged. This study documents the feasibility of near-continuous, non-destructive, measurement of renal vPO₂ and VO₂ by oxygen-dependent quenching of phosphorescence.