The mass transfer coefficients between solid particles and liquids in high aspect ratio contractors agitated by multiple impellers have been reported. Two vessel sizes i.e., 0.15 m and 0.30 m I.D. each with a length of 1.0 m were used. The effects of particle size, liquid viscosity and agitation speed were studied using two types of impellers, i.e., disc turbine (DT) and pitched turbine downflow (PTD). The spacings between two impellers were maintained at tank diameter. A simple mass transfer correlation based on critical suspension speed is proposed.