It is known to prepare olefin sulphonates by neutralizing olefin sulphonation products with dilute aqueous bases. This invention provides a method of preparing more concentrated solutions of certain olefin sulphonates by determining the position of the viscosity minimum which occurs at concentrations above the critical limit where gel formation is normally observed and which corresponds to the formation of a `G` phase, and reacting the olefin sulphonation product with the base in the presence of sufficient water to provide a product having a concentration corresponding substantially to this minimum.