Heat transfer coefficients were measured during film condensation of steam on horizontal tubes of 0.122, 0.182, 0.250, 0.375 inches in diameter. Scale effects were eliminated by repeated cleaning of the tubes. Filmwise, dropwise, mixed, and streaky condensation patterns of steam on the horizontal tubes were observed and photographed. The flow pattern in film condensation showed definite three-dimensional behaviour and was strongly affected by surface tension for the small tube diameters used. The measured heat transfer coefficients under film condensation showed differences as much as 50 percent from the two-dimensional analytical predictions. A dimensionless number representing the ratio of the surface tension force to the gravity force was obtained from a physical analysis. The experimental results showed that when the surface tension force was small in comparison to the gravity force., the surface tension force acts to suppress the heat transfer. When the surface tension and gravity forces were of comparable magnitude, the heat transfer was augmented. / Master of Science