This paper discusses the use of Lotus 123 spreadsheet software to design reservoir and production engineering applications that are easy to use and understand. Several of these applications have been created using a series of spreadsheet templates or subroutines that function as building blocks in developing larger petroleum engineering programs. These building blocks are based upon the algorithms available in industry publications that estimate properties of petroleum fluids. The design philosophy was to use algorithms whenever possible and to reduce the amount of input required by the engineer. It is hoped that demostrating this programming techniques, demonstrated in this paper, will lead to the development and exchange of application programs.