Abstract Background: Nasal CPAP introduces positive pressure of air into both trachea and stomach, which may affect gastric emptying. The rate of gastric emptying can be estimated by US by two validated techniques: “antral cross-sectional area” (2-dimensional estimate of the surface area at the gastric antrum), and “spheroid gastric volume” (3-dimensional estimate of the stomach content volume). No study examined gastric emptying rate in infants on bubble CPAP (bCPAP). Objective: To compare gastric emptying rates in neonates on machine-derived nasal CPAP (MD-nCPAP) with those on bCPAP. Methods: Ultrasound measurements of the amount of milk in the stomach were performed before feeding and at 1, 2, and 3 hours after the start of feeding, using both the ACSA and spheroid methods. Rates of gastric emptying were calculated during the “early” (1-2 hours) and “late” (2-3 hours) phases after feeding. Results: We recruited 32 infants (25-34 weeks gestational age). Seventeen infants were treated with MD-nCPAP [median birth weight 1015 g (IQR: 870 to 1300), gestational age 28 weeks (IQR: 27 to 29), postnatal age 20 days (IQR: 14 to 28)], while 15 infants were treated with bCPAP [median birth weight 960 g (IQR: 855 to 1070), gestational age 27 weeks (IQR: 26 to 28), postnatal age 17 days (IQR: 15 to 25)]. Gastric emptying rates (% emptied/min) were significantly faster in the “early” compared to the “late” phase for all infants. There were no significant differences in the rates of gastric emptying (either “early” or “late”) or volumes of gastric residuals between infants receiving MD-nCPAP or bCPAP, measured by either method. Conclusions: Gastric emptying is faster during the “early” compared to the “late” phase. Gastric emptying rates are not different in infants receiving MD-nCPAP vs bCPAP.