Mixed convection in single and double-lid driven horizontal rectangular cavities filled with a Newtonian fluid and subjected to uniform heat flux along their vertical short sides is studied numerically and analytically. The finite volume method with the SIMPLER algorithm is used to solve the full governing equations for which the Boussinesq approximation is adopted while the analytical approach lies on the parallel flow assumption, valid in the case of shallow enclosures. A good agreement between the two approaches is observed within the explored ranges of Peclet and Rayleigh numbers. The effects of such parameters on the flow and heat transfer characteristics are analyzed for both kinds of driven cavities. The zones characterizing the dominance of natural and forced convections as well as when the two phenomena compete (mixed convection) are delineated. It is found that the transition from one dominated regime to another depends on the ratio Ra/Pe(3). (C) 2018 Elsevier Ltd. All rights reserved.