This review article examines the pathophysiology of septic shock, with special attention to the concept of supply-dependent consumption and the implications this concept has for therapy. Patients with septic shock require higher levels of oxygen delivery (Do2) to maintain aerobic metabolism. When Do2 is inadequate, peripheral tissues switch to anaerobic metabolism and oxygen consumption decreases. The lactic acidosis that occurs is a reasonable clinical marker of supply dependency and inadequate tissue perfusion. Maximizing Do2 is an important part of the hemodynamic resuscitation of patients with septic shock. To achieve this goal, intravascular volume must be restored and the myocardial depression associated with sepsis must be treated to optimize cardiac output. The normalization of arterial lactate concentration is a reasonable goal of resuscitative efforts.