A gastric space filler device effective for reducing stomach volume comprises at least one inflatable space filler and a sleeve to prevent leakage out of the gastric space filler device. 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 and methods are effective for inserting a gastric space filler device into a patient. The gastric space filler device may be provided with sheaths and methods for covering the gastric space filler device during delivery into a patient.
