Experimental investigations were carried out to determine the convective heat transfer performance and pressure drop of Al2O3 /water and SiO2 /water nanofluids flowing through a circular tube. Measurements show that the addition of small amounts of nano-sized Al2O3 particles to the base fluid increases heat transfer coefficients considerably, while the result for the silica nanofluids contradicts with the alumina nanofluids and this leads to some interesting results. In the case of alumina nanofluids, an average increase of 16% in convective heat transfer coefficient is observed with an average penalty of 28% in pressure drop. Moreover, flow resistance increases significantly compared to the base fluid even at very low concentrations of nanofluids. Finally, measured heat transfer coefficients are compared with predicted ones from the correlation of Shah under the same conditions. Experimental investigations were carried out to determine the convective heat transfer performance and pressure drop of Al2O3 / water and SiO2 / water nanofluids flowing through a circular tube. Measurements show that the addition of small amounts of nano-sized Al2O3 particles to the base fluid thick heat transfer coefficients considerably, while the result for the silica nanofluids contradicts with the alumina nanofluids and this leads to some interesting results. In the case of alumina nanofluids, an average increase of 16% in convective heat transfer coefficient is observed with an average penalty of 28 %, in pressure drop. Moreover, flow heat resistance significantly significantly compared to the base fluid even at very low concentrations of nanofluids. Finally, measured heat transfer coefficients are compared with predicted ones from the correlation of Shah under the same conditions.