Feedstock injection is an essential step of the fluid catalytic cracking process in which complex phenomena take place, such as droplet formation and dispersion, liquid heat-up and vaporization. These phenomena greatly affect product and coke yields. Several models have been proposed to estimate the vaporization of feed droplets in the riser injection zone. However, depending on the assumptions on which the model is based, completely different vaporization times may be predicted. No experimental validation exists to discriminate between the various models. This paper presents the first method for the accurate measurement of the vaporization kinetics of a liquid spray injected into a hot fluidized bed. The droplet size has a very strong effect on the vaporization. With a droplet size of 60 mum, it takes about 100 ms to vaporize 50% of the liquid: with a droplet size of 30 mum, this time is cut by half. (C) 2003 Elsevier B.V. All rights reserved.