Mixing is a common unit operation and there are a great variety of the possible systems to be mixed and the configurations to be applied. All this makes the selection of mixing equipment as an important field for the expert systems application.This paper presents the spreadsheet-based expert system for the selection of stirred tank vessels. The presented system has been designed to work in the narrow field of expertize. The general methodology of the mixers selection is presented first. The program structure and the implementation aspects are discussed further. The last part of the paper presents the example of the system application, comments about the obtained solutions and summary.The expert systems implemented in spreadsheet programs are not very popular and there is a common believe that their capabilities are strongly limited. However, our experience proved that this type of expert system could be very useful in the equipment selection. We recommend the development of the expert systems starting from the specialized tools and next transfer of the structured knowledge systems into spreadsheet programs.