In this article, the numerical investigation of entropy generation due to heat transfer irreversibility and fluid friction irreversibility during natural convection within tilted square cavity with hot wall AB, cold side walls (DA and BC), and top insulated wall (CD) has been performed. The numerical simulation has been carried out for various fluids of industrial importance (Pr = 0.015, 0.7, and 1000), Rayleigh numbers (10(3) <= Ra <= 10(5)), and different inclination angles (phi = 15 degrees, 45 degrees, and 75 degrees). The results are presented in terms of isotherms (theta), streamlines (psi), entropy generation maps due to heat transfer (S-theta), and fluid friction (S-psi). The total entropy generation (S-total), average Bejan number (Be-av), and average heat transfer rate ((Nu) over bar (AB)) are plotted for Rayleigh number 10(3) <= Ra <= 10(5). The maximum values of S-theta occur near the corner regions of wall AB due to a junction of hot and cold walls. On the other hand, maximum values of S-psi, are found near the walls of the cavity due to friction between the circulation cells and walls of the cavity. It is found that minimum entropy generation occurs for phi >= 45 degrees at convection dominant mode (Ra = 10(5)) for lower Pr (Pr = 0.015 and 0.7). The inclined cavity with phi = 45 degrees may be an alternative optimal inclination angle in optimal thermal processing of high Pr (Pr = 1000).