We disclose apparatus and methods for delivering for patient infusion or other use two or more fluids either sequentially or simultaneously. The apparatus has a fluid delivery compartment containing a first infusion fluid, a flexible membrane, and an openable bag containing a second infusion fluid. An attached gas reaction compartment contains chemical reactants which, when combined, react to evolve gas. The gas expands a gas expansion chamber causing the membrane to move into the fluid delivery compartment, displacing the first infusion fluid. The membrane eventually contacts and compresses the openable bag. Pressure from the membrane causes the bag to open and discharge its contents out of the infusion device.