Minderman, Peter A.McAvoy, Thomas J.Gasner, Larry L.Previous investigators have demonstrated the theory and applications of macroscopic elemental and material balances to the estimation of bioreactor states. However most previous applications have been limited to processes which have only one growth phase. An expert systems knowledge base is presented which is used to extend this empirical estimation technique to procesess which have multiple phases (e.g. a lag phase, a growth phase, and a production phase). This approach is illustrated by a simple example from the literature.en-USTechnical Report