An inflatable retention system for an enteral feeding tube having a base deployed outside the human body and an indwelling retainer which is deployed within a lumen or cavity of the body by insertion through a stoma from outside the body. The retention system includes a tube having a proximal end, a distal end, an external tube diameter, and tube walls defining a feeding lumen and an inflation lumen. The retention system also includes an inflatable balloon located at a distal end of the tube in fluid communication with the inflation lumen, the balloon having thin, flexible walls, a predetermined spheroid shape, and a volume at which a fluid in the balloon is under no pressure such that upon inflation with a fluid to pressurize fluid in the balloon, the balloon assumes a stable spheroid shape and exhibits a substantially linear pressure versus volume curve.