SHIM (the Shell Isomerization Model) performs a rigorous kinetic simulation of a C5/C6 paraffin isomerization unit. The Hysomer and ParIsom technologies are fully supported. Penex support is very limited and SHIM should not be applied to Penex units. The core of the program is a theoretically based model of the reaction kinetics in an isomerization unit. As such, a properly tuned model can accurately predict the effect of changes in feedstock or operating conditions even when they are well removed from "normal" operation. This provides a basis for rigorous unit monitoring as well as an efficient means of exploring opportunities and ideas as they arise. Typical uses of the model include the following: Performance evaluation of existing isom units. Optimization of unit operation. Evaluating the effect of different feedstocks.