Technical Abstract: OBJECTIVES: To determine whether osmolality, volume, or energy density affects gastric emptying rate (GE); whether simultaneously decreasing osmolality and increasing volume accelerates GE; and whether GE is related to any clinical and/or demographic characteristics. STUDY DESIGN: GE was measured using the (13)C-octanoic acid breath test in 17 infants of 25 to 30 weeks gestation in a tertiary care children's hospital. In study 1, the independent effects of osmolality, volume, and nutrient density were evaluated in 10 infants. In study 2, the combined effects of decreasing osmolality and increasing volume were evaluated in 7 infants. Results from all infants were used to investigate the relationships between clinical and demographic characteristics and GE. The statistical analysis comprised analysis of covariance, the (paired) Student t-test, the 1-sample Wilcoxon test, and regression analysis. RESULTS: Mean (+/- standard deviation) age was 27.7 +/- 14.6 days in study 1 and 34.1 +/- 14.0 days in study 2. Altering osmolality, volume, or energy density did not change GE, but simultaneously decreasing osmolality and increasing feeding volume accelerated GE by 18% versus standard feeding. GE correlated with gestational age at birth. CONCLUSIONS: Unlike in adults, in preterm infants osmolality, volume, or energy density individually do not affect GE. Reducing osmolality and increasing feeding volume increases GE. GE is related to gestational age at birth even at age 1 month.