Nucleate subcooled pool boiling of water over vertical steps was carried out under atmospheric conditions. Two forward-facing steps of 0.8125 and 0.50 in. were considered. Data were statistically analyzed to determine samplingerror.Theebullitionwasqualitativelyexplainedintermsofthermal/e owe eldsandbubbledynamics.Plots of boiling heat e ux vs superheat and surface heat transfer coefe cient vs heat e ux have been provided. Empirical correlations, developed from the above-mentioned data, are also presented. Boiling on vertically extended surfaces showed an increase in heat e ux for a given superheat when compared with a plain vertical surface because of e uid agitation in the region of the step. The parameters associated with bubble dynamics and bubble interactions were also qualitatively discussed. Nomenclature C = correlation constant h = surface heat transfer coefe cient, kW/m 2 K n = exponential constant q = ebullition heat e ux, kW/m 2 T = temperature, K Subscripts p = pool conditions w = wall conditions