According to features of the present disclosure, a gastric space filler device (19) and exemplary methods effective for reducing stomach volume are disclosed. A gastric space filler (19) comprising at least one inflatable space filler (91A, 91B) and a sleeve (110A, 110B) to prevent leakage out of the gastric space filler device is disclosed. The gastric space filler device may be inflated with an insufflation fluid and with mineral oil, which further has the effect of reducing leakage. Delivery systems (200) and exemplary methods for inserting a gastric space filler device into a patient are also disclosed. Sheaths (202) and exemplary methods for covering a gastric space filler device during delivery into a patient are also disclosed.
