Underwater lift bags (ULB's) are flexible parachute like devices filled with air to recover objects from underwater. ULB's can exhibit uncontrolled ascent rates which are problematic. A theoretical model of ULB performance was developed and supported experiment design, but did not accurately predict performance of ULB's due to unknown values for several parameters and the nature of ULB failure modes. The performance of a ULB under multiple loading and initial release conditions was documented. Testing confirmed one known failure mode of collapse during rapid ascents and documented another failure mode. A correlation between ULB loading and maximum ascent velocity was developed. A critical ascent velocity was derived based on ULB envelope height. A relationship between envelope height and load fraction to prevent ULB collapse was also developed. A method of adjusting maximum ULB capacity in-situ to avoid failure from excessive rates of ascent due to low loading was successfully tested.