Particle formation during fluidized bed spray agglomeration is modeled by a Monte Carlo method. The methodology is based on the micromechanisms occurring within the bed. The most important model parameters are identified as interparticle collision time, deposited droplet drying time and droplet addition time. It is found that a high number of collisions leads to a negligible role of the drying mechanism. In the real bed, however, the process is dependent on the gas inlet temperature. This indicates that the number of collisions relevant to agglomeration is relatively low. The accordance of the model with experimental results for variations of several process parameters demonstrates that the approach is a promising way to simulate the formation of agglomerates. In addition, the model is able to reproduce slower agglomeration at increased temperatures. This result is, for the first time, based on physical mechanisms rather than on the use of fitted agglomeration kernels. (C) 2011 American Institute of Chemical Engineers AIChE J, 57: 3012-3026, 2011