Mass transfer rates to and from drops in liquid-liquid extraction equipment are often likely to be reduced by the presence of surface active contaminants. For industrial column design circumstances it is ideally required to account for the extent of contamination in a quantitative manner yet existing design procedures do not allow this to be done for the typical intermediate Reynolds number region of 10 to 100. A method is proposed for correcting continuous phase and drop mass transfer coefficients for the deleterious effects of contamination using only one contamination parameter which needs to be determined experimentally.