A technique for characterizing the stability of two-phase sprays is reported in this work. The method has been validated by high-speed visualization, and tested for a variety of feed nozzles and test fluids in both open-air and in a gas -solid fluidized bed. The results indicate that the two-phase flow pattern in the conduit leading up to the nozzle strongly influences the spray stability. In this regard, the predictions from the Taitel and Dukler [161 [Y. Taitel, A.E. Dukler, A model for predicting flow regime transitions in horizontal and near horizontal gas-liquid flow, AIChE J. 22 (1976) 47-55.] flow map are in good agreement with the present characterization. Locating a liquid-line restriction, ahead of the two-phase mixing region in the conduit, appears to create an induced bubbly flow, which significantly improved the spray stability by delaying the onset of slugging. It is also believed that the above effect was a consequence of having a shorter conduit section, where fully developed flow did not exist. An important finding from this study suggests that the spray stability is unaffected for injections in both open-air and in a gas-solid fluidized bed. Moreover, strong correlation between the upstream (in the conduit) and downstream (in the spray region) fluctuations was observed by the stability detection probes. The present technique can be easily accommodated for on-line monitoring of nozzles in applications like fluid coking, where the nozzle performance strongly affects the process efficiency. (c) 2005 Elsevier B.V. All rights reserved.