A fundamental physical mechanism whereby sprays are formed from liquid jets is formulated. It is shown that a combination of axial disturbances cannot produce the necessary conditions for nonaxial evolution of drops. These conditions are satisfied by a nonaxial sequence of superimposed disturbances, propagating one on top of the other. The resulting model is used to describe the evolution of liquid jets into sprays. It is postulated that every consecutive superimposed disturbance, which is characterized by a self-instability parameter, travels tangent to the surface that supports its propagation. Model outputs show that starting from the first superimposed disturbance, highly complex profiles of the jet surface are generated. Fourier analysis of the derived superimposed disturbance functions is performed in conjunction with the basic building blocks of classic instability theory. This is achieved by assigning to each term a self-instability factor. The sum of these building blocks results in intricate profiles of the jet. In these profiles, multiplicity of radial position of the jet interface as a function of axial distance provides the necessary conditions for evolution of nonaxial drops. The model accuracy, which depends on the disturbance rank, is sufficient to disclose the mechanism that turns the jet into a spray. The observed jump in the level of error is commensurate with the sudden increase in flow complexity that follows an increase in the disturbance rank. Finally, model outputs are used to study the effect of instability parameters on the evolution patterns of the jet and the nonaxial discharge of drops. (C) 2003 Elsevier Science (USA). All rights reserved.