Summary Plug cementing is still considered to be a critical operation, and cases of failure eventually happen. A large annular gap and eccentricity, typical of these operations, are factors that may promote unstable flows, resulting in cement-slurry contamination. Deepwater conditions enhance chances of free fall, and, consequently, low displacement velocities can occur in the annulus. This article presents a parametric study of the role of rheological properties of fluids (drilling fluid, spacers, and cements slurries), string rotation, and flow rates (including free-fall effects) in the displacement quality of cement plugs. Analyses are based on two different simulation tools. Conventional cement-pumping software defines flow-rate profiles at the annulus entrance, accounting for free-fall effects, and computational fluid dynamics (CFD) simulates the interface propagation and contamination levels. The main issues addressed by the simulations are What are the maximum yield stresses that guarantee nonstagnation regions while circulating the drilling fluid?How can one optimize density and rheology hierarchy, which minimizes contamination and avoids channeling?What is the role of string rotation on the displacement efficiency? The compilation of simulation results into useful guidelines and procedures for displacing cement plugs in vertical, inclined, and horizontal offshore wells is presented.