AbstractA wetted‐wall column is used to determine the values ofHOLandKLa for the flow of a viscous cuprous ammonium lactate solution countercurrent to a H2/CO gas mixture.Kapitsa's equation is used to calculate the value of the interfacial area on the rippled liquid surface. Values ofKLare calculated and the effects of liquid and gas flow onKLare determined. It is shown that there is a significant effect of gas flow even though the absorption is liquid film controlled.With a viscous solution the wetted‐wall column can simulate conditions in a packing. The results from the wetted‐wall and packed towers are examined by a new method to obtain the degree of wetting of the packing while mass transfer is occu