Venous oxygen saturation has been traditionally used as a marker for tissue hypoxia. A wide range of factors can affect it. Literature abounds with articles on the use of the same in decision making and clinical management of patients in shock. Likewise, the application of venous saturation in patients undergoing cardiac and noncardiac surgery has been demonstrated. The controversy as to whether superior vena cava oxygen saturation can replace the traditional mixed venous oxygen saturation is never ending. Irrespective of the body of evidence, it is recommended that clinical decision should not be based on a single value, and a range of values needs to be incorporated to differentiate a critically ill from a noncritically ill patient.