The effects of Reynolds and Prandtl numbers on the heat transfer characteristics of an unconfined sphere for different thermal boundary conditions (isothermal and isoflux) on the sphere surface have been investigated numerically by using a finite volume method for the range of conditions as 5 <= Re <= 200 and 0.7 <= Pr <= 400 (the maximum value of Peclet number being 2000). Based on the numerical results obtained herein, heat transfer correlations are developed for the constant temperature and the constant heat flux boundary conditions on the solid sphere surface in the steady symmetric flow regime. The variation of local Nusselt number on the sphere surface shows the effect of Prandtl number on heat transfer from a sphere in this flow regime. In addition, this work also demonstrates an approach to solve such flow problems using the Cartesian form of the field equations. (c) 2005 Elsevier Ltd. All rights reserved.