The influence of particle lyophobicity on gas hold-up, homogeneous to churn-turbulent regime transition, and gas-liquid mass transfer is investigated in a 0. 15 m diameter slurry bubble column at pressures from 0. 1 to 1.3 MPa. An air/nitrogen mixture is bubbled through 0-3 vol% slurries of activated carbon particles or silica particles suspended in demineralized water or organic oil Isopar M. The gas hold-up and flow regime transition point are not influenced by the presence of lyophilic particles. Lyophobic particles shift the regime transition to a higher gas velocity and cause foam formation. The gas-liquid mass transfer coefficient is proportional to the gas hold-up for all investigated slurries and is not affected by the particle lyophobicity and the operating pressure. A correlation is presented to estimate the gas-liquid mass transfer coefficient: k(l)a(l)/epsilon(g) = 3.0 root Du(b)/d(b)(3). (c) 2006 Elsevier Ltd. All rights reserved.