The present work focuses on the effects of multiple geometric perturbations on the three-dimensional buoyancy-driven flow and heat transfer in an annular cavity with impermeable end walls. The three-dimensional (3-D) study carried out involved the fluid flow and heat transfer analysis in a horizontal annulus with multiples of geometric perturbations placed on the inner cylinder of the annulus. The flow field structure corresponding to these different perturbations is analyzed. Heat transfer results were obtained up to a Ra of 10(4), and the heat transfer effects were studied by analyzing the local and average Nusselt numbers. It is observed that with the introduction of multiple perturbations on the inner cylinder, the overall heat transfer rate increases substantially. For example, the average Nusselt number at a Ra of 10(4) for the annulus with four perturbations was found to be about 25% higher than that for the annulus with a single perturbation, which itself was about 50% higher than that for the annulus without any perturbation. It was found that the average Nusselt number could be correlated as Nu = 0.71 Ra-0.1(1+0.12P), where P refers to the number of perturbations on the inner cylinder. The results show an interesting method for substantially augmenting heat transfer within an enclosed annulus.