To determine the magnitude and duration of the excess post-exercise oxygen consumption (EPOC), five obese (OB) and five normal weight (NW) women were studied following steady state and interval type exercise. Each subject completed a maximal treadmill test followed by 2-36 minute exercise trials, one at 60% VO2 maximum and one interval type trial alternating 30% and 90% VO2 maximum. Open-circuit spirometry was used to measure V02 before during and after exercise. There was no significant difference in exercise energy expenditure between groups or between the two exercise trials. Oxygen consumption remained elevated longer (p=<0.05) following the 30/90% trial (37.5± 21.5 minutes) than the 60 % trial (16.5± 4.7) for both groups and was almost twice as long for the OB group vs. the NW group (48 vs 27 minutes). V02 measures during the first 15 minutes after the 30/90% trial were significantly elevated (p=<0.05) above those for the 60% trial. When expressed in kcals this amounted to 17.4 ± 6.3 for the 30/90% trial and 9.0 ± 1.9 kcals for the 60% trial. The magnitude of the EPOC did not vary significantly between the 2 groups. The EPOC/ exercise oxygen consumption ratio was greater for the 30/90% trial (7.4% ± 2.3) compared to the 60% trial (3.9% ± .79). These finding suggest a larger EPOC may be created by doing interval type exercise compared to steady state exercise of similar energy expenditure. Although the EPOC was of longer duration for the OB group there was no difference in the magnitude of the EPOC between the groups.