In this study, heat transfer coefficients and pressure drops of R-134a inside round and flat tubes are investigated experimentally with mass flux of 450, 550, and 650 kg m(-2) s(-1) at saturation temperatures of 35 degrees, 40 degrees, and 45 degrees C. The effects of mass flux and saturation temperature on heat transfer coefficient and pressure drop are examined. The maximum enhancement factor and pressure drop penalty are obtained by flat tube (FT-2) up to 2.101 at 450 kg m(-2) s(-1) and 3.01 at 650 kg m(-2) s(-1), respectively. The correlation for flat tubes is proposed to predict the heat transfer coefficient within +/- 20% error.