Which systemic vein has the highest oxygen saturation?

Which systemic vein has the highest oxygen saturation?

Renal vein has the highest oxygen saturation. Hence the inferior vena caval blood is more saturated than superior vena caval blood. The saturation is higher in the inferior vena cava above the renal veins than the low IVC. Renal blood flow is much more than the metabolic requirement of kidney, meant for its filtration function, usually about one fifth of the cardiac output. Lowest oxygen saturation is in the coronary sinus. That is because oxygen extraction at rest is maximum in heart muscle.