Dark ground optical microscopy, electron microscopy, and protein release rate studies have been used to quantify the effects of formulation changes on the phase inversion dynamics and in vitro drug release properties of an injectable PLGA-based drug delivery system. Gel growth rates and water influx rates are determined from plots of the square of the respective front with time. Results show that additives that increase the solution gelation rate and produce finger-like void morphologies result in higher initial release rates. Conversely, additives that slow the rate of gelation dramatically reduce the initial drug release rate and lead to a more dense sponge-like morphology.