Blending is a complex process. There is a basic equation involved in this process. It is a nonlinear process. There are different sources of error in this process. There are assumptions about blending equations. This process depends on a component’s chemical characteristics and the availability of stock. This topic will discuss factors behind the complexity of the blending process, blending as a nonlinear process, steps to match blending with reality, sources of errors, a basic blending equation, first step linearization, non-linear blend models, type-II blend nonlinear models, etc.