Abstract: A nursing bottle having a body, a flexible liner, and a feeding nipple. In one embodiment, the body includes a check valve to allow air into a chamber formed between the body and the flexible liner to equalize the pressure in the chamber and prevent air from leaving the chamber. This prevents the liner from expanding and air from reentering the liner. Other embodiments of the nursing bottle include a pump for introducing pressurized air into the chamber and thereby expelling air from the liner. In still other embodiments, the bottle comprises a two-part body in which the parts of the body are slidably and sealably engageable with each other wherein movement of the parts relative to each other pressurizes the air in the chamber and expels air from the liner. Disclosed are also methods of feeding an infant or animal utilizing such nursing bottles.