The accuracy of using linear models for crude distillation unit (CDU), fluidize-bed catalytic cracker (FCC) and product blending in refinery planning has been debated for decades. Inaccuracy caused by nonrigorous linear models may reduce the overall profitability or sacrifice product quality. On the other hand, using rigorous process models for refinery planning imposes unnecessary complications on the problem because these models lengthen the solution time and often hide critical issues and parameters for profit improvements. To overcome these problems, this paper presents a refinery planning model that utilizes simplified empirical nonlinear process models with considerations for crude characteristics, products' yields and qualities, etc. The proposed model can be easily solved with much higher accuracy than a traditional linear model. This paper will present how the CDU, FCC and product blending models are formulated and applied to refinery planning. Several case studies are used to illustrate the features of the refinery-planning model proposed. (c) 2005 Elsevier Ltd. All rights reserved.