This paper describes the prototype of a hybrid expert system; Slip Expert is used for estimating the slip velocity of multiphase flow in a producing well. The system consists of five components: OSF/Motif based front-end user interface, inference engine, knowledge base, model base, and preprocessor. The user inter- face is used to input control parameters and curve data. Rules derived from charts, empirical models, and log analysts’ expertise are contained in the knowledge base. The inference engine controls the reasoning process and computes oil and/or gas slip velocities until the predefined goals are satisfied at each selected station or depth. Charts and equations used to estimate slip velocities are contained in the model base, and the preprocessor provides starting slip values for the reasoning process. Case and com- parison studies show that the resulting profiles using this system are in good agreement with the raw data, and the expert system is superior in all cases to the other models used for comparisons.