An inflatable retention system for an enteral feeding tube has a base deployed outside the human body and an indwelling retainer which is deployed within a lumen of the body by insertion through a stoma from outside the body. The retention system comprises a tube having a proximal end, a distal end, an external tube diameter, and tube walls defining a feeding lumen and an inflation lumen, and an inflatable balloon located at a distal end of the tube in fluid communication with the inflation lumen. The balloon has thin, flexible walls, a predetermined spheroid shape, a reserve volume having a lower limit that is greater than 0.5 milliliters of a fluid and an upper limit at a transition between a non-distended state and a distended state of the balloon in which a fluid in the balloon is under no pressure, and a predetermined fill volume about 1.01 to about 1.5 times greater than an upper limit of the reserve volume. 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 to at least the predetermined fill volume.
