The operation of blast furnaces with coal/natural gas injection requires high coke quality. For lowest coke cost while keeping the necessary coke quality, the choice of coals and the formulation of the blend is a very important issue. A widely utilized tool for blend design is modeling, preceded by coal characterization and followed by pilot oven testing. In this paper, the development of models is reviewed, based on public literature. Three main stages are taken into account, form the sixties to current times.