The purpose of this study was to develop a simple, convenient and indirect method for predicting peak oxygen uptake (VO2peak) from a sub-maximal graded exercise test (GXT), in obese women. Thirty obese women performed GXT to volitional exhaustion. During GXT, oxygen uptake and the power at RPE 15 (VO2peak) were measured, and VO2peak was determined. Following assessment of the relationships between VO2peak and PRPE 15, age, height and mass were made available in a stepwise multiple regression analysis with VO2peak as the dependent variable. The equation to predict VO2peak was: (1 min-1) = 1.355 - 9.920e-3 x age + 8.497e-3 x PRPE 15 (r = 0.83; SEE = 0.156 l min(-1)). This study suggests that age and PRPE 15 elicited during a sub-maximal GXT provides a reasonably accurate prediction of VO2peak in obese women.