This paper describes a new multiphase reactor, the rotor-stator spinning disc reactor, which shows high rates of gas-liquid mass transfer in comparison to conventional multiphase reactors. The volumetric gas-liquid mass transfer coefficient k(GL)a(GL), in the rotor-stator spinning disc reactor increases with increasing rotational disc speed, due to the higher surface renewal rate caused by the increasing turbulence, and with increasing gas flow rate. Measured k(GL)a(GL). values are as high as 0.43 m(L)(3) m(R)(-3) s(-1) at 7.3 x 10(-6) m(3) s(-1) gas flow and a rotational disc speed of 179 rad s(-1), and are expected to increase even further at increasing rotational disc speed. This is twice as high as for conventional reactors as bubble columns, in spite of the low gas holdup of 0.021 m(G)(3) m(R)(-3) with only one gas inlet. The volumetric mass transfer per unit volume of gas, k(GL)a(GL)/epsilon(G), of 20.5 m(L)(3) m(G)(-3) s(-1) is 40 times higher than 0.5 m(L)(3) m(G)(-3) s(-1) for a bubble column. (C) 2009 Elsevier Ltd. All rights reserved.