To identify effects of the inclination angle oil pool boiling heat transfer all experimental study has been executed. For the test a single tube of 30 mm diameter and all annulus of 12.7 mm gap size submerged ill the saturated water at atmospheric pressure have been considered. The inclination angle changes heat transfer much. The change of the inclination angle from 0 degrees to 45 degrees results in 29.8% and 11.2% decrease in the heat transfer coefficient at 40 kW/m(2) for the single tube and the annulus, respectively. For the single tube, no specific changes in heat transfer are observed as the inclination angle increases Lip to 15 degrees whereas the angle for the annulus is 30 degrees. The major heat transfer mechanisms arc considered as the intensity of liquid agitation and bubble coalescence due to the enclosure by the outer tube. (C) 2008 Elsevier Ltd. All rights reserved.