A quasi-ARMAX modelling scheme is studied for the purpose of modelling and control of multi-variable ill-conditioned and nonlinear processes. A distillation column is used as a case-study. The modelling technique is in this paper extended for use in the multi-variable case. Also, the nonlinear directionality of the distillation column is analyzed and illustrated. The nonlinear MPC formulation with the quasi-ARMAX model used for prediction is studied for control of the distillation column at different operating regions. (C) 2004 Elsevier Ltd. All rights reserved.