In this study, wax deposition in horizontal well bores and vertical well bores is compared. In a vertical well, the temperature change is the dominant mechanism for wax deposition; however, in a horizontal well, the main mechanism for wax appearance is the pressure change. Six different thermodynamic models, developed originally for vertical wells by other researchers, were improved for horizontal wells by modifying with a pressure function, and a computer program was developed to simulate the precipitation phenomena in vertical and horizontal well bores. Solid-liquid equilibrium constants for each pseudo-component were calculated. Critical pressures and overall solid mole fractions of the crude oil at different error ranges were determined. It was observed that wax is precipitated mostly in vertical sections, and the pressure change had a minor effect on wax appearance in horizontal sections.