This report describes the work performed by Physical Sciences Inc. (PSI) in the development of a Fluidized Bed Coal Gasifier/Systems Model. The program was performed in two tasks. The first task is concerned with the modification of the existing PSI/FLUBED code to account for the possibility of slug flow in the gasifier. Work previously performed under the present contract indicated that the Westinghouse PDU gasifier operated in the slug flow regime. Prior to this time the PSI/FLUBED code modeled ebullating beds only. The second task performed under this contract has been concerned with the development of a systems model which simulates the operation of a commercial scale Westinghouse Fluidized Bed Coal Gasifier. The systems model is based on the output of 33 reference states developed by running the PSI/FLUBED code. Under this task, the systems model was developed along with two supporting codes for checkout and data file preparation. The data from the PSI/FLUBED code was reviewed and 180 Taylor series expansion coefficients were generated. In addition the PSI/FLUBED code was modified to handle gasifiers whose diameter varies discontinuously with height. An interface driver was also developed which streamlines the operation of the PSI/FLUBED code making it more user friendly. All codes developed under the contract have been verified and are operational. 14 references, 4 figures, 9 tables.