fax 01-972-952-9435. AbstractThis paper presents a semi-analytical solution for the pressure drawdown of horizontal or deviated wells in an infinite reservoir considering the well as a source of infinite conductivity. The solution is obtained using the concept of Green's functions applied to solve the diffuse equation in radial coordinates for a point in an infinite domain kept at a constant pressure. The solution is employed to generate dimensionless functions in order to investigate the behavior of horizontal or slanted wells. Others analytical solutions available in the Literature are used for validation and comparison of results. Calculation procedures are illustrated in the Appendix A and B at the end of the paper.