Subcooled film boiling has been investigated experimentally for vertical up-flow in a directly heated tube using the refrigerants R-12, R-22 and R-134a as test fluids. The data cover a mass flux range of 530-3000 kgm(-2) s(-1), an inlet subcooling range of 8-28 degrees C and a pressure range of 0.83-1.6 MPa (corresponding to an approximate water pressure range of 5-7 MPa, based on an equal liquid-to-vapour density ratio). To the authors’ knowledge, these are the first flow film boiling data obtained for R-134a and R-22. The results show strong effects of mass flux, inlet subcooling and pressure on the heat transfer coefficient. Also, the data exhibit complex trends of the heat transfer coefficient as a function of thermodynamic equilibrium quality. Because of the wide range of conditions covered in this study, a systematic examination of the effect of flow parameters and fluid properties on the heat transfer coefficient was performed, and this has provided a unique insight into the heat transfer mechanisms.