The aim of this study is to combine the basic concepts of mechanics on drill string which are related to directional drilling, thus finding a less complicated and more economical way for drilling directional wells. Slick BHA, which has no stabilizers attached and single stabilizer BHA are analyzed through previously derived formulas gathered from the literature that are rearranged for this study. An actual directional well is redrilled theoretically with a slick BHA and a computer program is assembled for calculating the side force and direction of the well for single stabilizer BHA. Influence of controllable variables on drilling tendency is investigated and reported. The study will be useful for well trajectory and drill string design in accordance with the drilling phase. Also, by using available data from offset wells, drilling engineer can back-calculate the formation anisotropy index (FAI) that is often used for optimizing well trajectories and predicting drilling tendency on new wells in similar drilling conditions. After analysing the directional well data used in this study, it has been concluded that the well could be drilled without a steerable tool if the kick of point (KOP) is not a shallower depth. If the KOP is kept similar, the same curvature could not be achieved without a steerable tool.