Overall mass transfer coefficients (OMTCs) during membrane solvent extraction (MSE) for a microfiltration membrane Accurel, an organic solvent nanofiltration (OSN) membrane MPF 50, and silicone rubber were investigated with a hydrophilic solute (phenol) and a hydrophobic solute (toluene) in a membrane solvent extractor. Decanol was used to extract phenol or toluene from water. In MSE of phenol from water, MPF 50 has an OMTC intermediate between Accurel and silicone rubber, and has a much higher breakthrough pressure than Accurel. For MPF 50, it was observed that the solute-membrane interaction makes a major contribution to the mass transport of hydrophobic compounds, such as toluene, through the membrane. This suggests that solution-diffusion type models may be more appropriate than pore-flow models for describing transport of solvents through these kinds of membranes.