This study presents the development of a new spray model that captures the full polydisperse nature of spray flow without using drop size classes. In this model, the size information concerning the spray is obtained by calculating three moments of the drop size distribution function from transport equations and one moment from a Gamma distribution function. The method reduces the need to presume a particular distribution function for the drop sizes and the complexity of the solution scheme. Drop size data obtained from the examination of the structures of a free spray using a laser-diffraction-based drop analyzer were used to further develop the new spray model and determine its ability to accurately predict such sprays. Test results include the axial distributions of the radial-averaged drop sizes and the local drop distribution at axial positions, and indicate that the drop size distribution is dependent on the atomizing air pressure of the injector and the position of the drop from the injector nozzle. At higher pressure cases the distributions were observed to be bimodal. These trends are captured by the computational results and compare well with those from another moments spray model.