A Layered reservoir system with a constant pressure bottom boundary has immense potential to produce oil and gas, using horizontal wells may further increase productivity because it offers a larger surface area for fluid withdrawal. Test analysis in this system is tedious, time consuming and interpretation may be confusing or erroneous. Hence an efficient algorithm is needed to generate accurate pressure response of the wells to facilitate quick and easy analysis and prediction. This paper presents an interactive computer program that computes the dimensionless pressure and dimensionless pressure derivatives of horizontal wells in a two layered reservoir system with a constant pressure boundary. Program's codes and structure of the reservoir model solution were written utilising the exponential integral solution, Gauss Laguerre and Gauss Lagrange numerical methods. The program has features that gave visual interpretation (graphical user interfaces (GUI)) as it computes pressure and derivative values when the interface between the layers is either permeable (crossflow reservoir) or impermeable (no crossflow reservoir). Examples illustrating its use in model identification and well test analysis of layered system with constant pressure boundary are also included in this work. Hence it will serve as a good learning tool because it is user friendly, fast and results have acceptable level of accuracy.