Abstract: The present invention relates to a continuous process for the quaternisation of tertiary amines with an alkyl halide. The process is performed at a temperature between 50° C. and 140° C. by reacting a tertiary amine and an alkyl halide in a tubular reactor at a pressure sufficient to keep the alkyl halide dissolved in the reaction mixture. The molar ratio between the tertiary amine and the alkyl halide is from 1:1.3 to 1:2.9 and the pressure is suitably between 12 to 65 bar. The process could be performed either with or without a solvent present, preferably without a solvent. The process gives high product yields and low amounts of by-products.