OBJECTIVE To quantify energy expenditure of various lifestyle physical activities of obese, overweight, and normal-weight girls. METHODS In total, fifty-five girls participated in six activities: a treadmill walk at 4.0 km x hr(-1), run, football throw, walk in open area, cycle, and riding a scooter. Intensities for all activities except the treadmill walk were self-selected. Energy expenditure was measured using the COSMED K4b(2) portable metabolic system. Analyses of variance were used to compare the three groups (obese n = 11, overweight n = 16, and normal weight n = 28) on relative VO2 (ml x kg(-1) x min(-1) and ml x FFM(-1) x min(-1)), and absolute energy expenditure (kJ x min(-1)). Magnitudes of the mean differences were examined using Cohen's delta (ES). RESULTS Relative VO2 (ml x FFM(-1) x min(-1)) was not significantly different (p > 0.05) among the groups for any activity. Obese girls expended more energy (p < 0.05) than normal-weight girls on all weight bearing activities. These differences were large (ES > or = 0.91). The differences in kJ x min(-1) between the obese and normal weight groups for the bicycle and scooter activities were moderate to large (ES > or = 0.56), although not statistically significant. The overweight group expended more energy than the normal weight group and less energy than the obese group on all activities (ES = 0.17 to 1.82), although these differences were generally not statistically significant. CONCLUSIONS The oxygen costs of various activities are similar among obese, overweight, and normal-weight girls when expressed relative to fat-free mass. When engaging in self-selected levels of activity, obese girls have a higher absolute energy expenditure than normal-weight girls.