Background and Objectives: Energy expenditure in severe sepsis/septic shock patients was measured by indirect calorimetry and the correlation of energy expenditure between indirect calorimetry and predictive equations was determined. Methods and Study Design: This was a prospective, observational analytical study. Severe sepsis or septic shock patients were measured for energy expenditure over 72 hours by indirect calorimetry that was measured by a mechanical ventilator (EngströmCarestation, GE Healthcare). Predictive equations for energy expenditure by the Harris-Benedict equation (HBE), Ireton-Jones 1992 equation (IRE) and ACCP equation (ACCP) were calculated and then correlations and agreement between indirect calorimetry and predictive equations were tested. Results: The 16 patients had a mean age of 71.6±5.5 years and a mean APACHE II score of 26.9±4.0. The average energy expenditure by indirect calorimetry over 72 hours per kilogram body weight was 26.7±5.3 kcal/kg/day. For predictive equations, IRE was moderately significantly correlated with indirect calorimetry over 72 hours (intraclass correlation 0.46, 95% CI -0.01 to 0.77, p=0.028), but the HBE and ACCP equations were not significantly correlated (intraclass correlation for HBE -0.52, 95% CI -0.8 to -0.06, p=0.985 and intraclass correlation for ACCP 0.29, 95% CI -0.21 to 0.68, p=0.121). Conclusions: Energy expenditure over 72 hours in severe sepsis or septic shock was about 26.7±5.3 kcal/kg/day. The use of predictive equations should be further examined in future studies.