Abstract: An improved osmotic engine is disclosed. The osmotic engine is adapted to be used with an osmotically driven syringe which can be used to deliver a beneficial agent, such as a drug, at a pre-determined rate over an extended period of time. The osmotic engine has an exterior wall defining a compartment which contains an osmotic solute. The wall comprises a thin permeable and/or microporous material which is permeable to an external fluid such as water but is impermeable to the solute. The wall also has a delivery orifice drilled therethrough. A rigid non-dissolving ring-shaped wall support is provided for maintaining the shape of the engine during use. The wall support also provides an open fluid flow path extending from the semipermeable wall portion toward the delivery orifice. The open fluid flow path minimizes the time required for the engine to begin pumping.