Correlations for the estimation of density and viscosity in mixtures of lauryl alcohol and its sulphonation product, laurylsulphuric acid, are given. These correlations depend on temperature and conversion, expressed as acid molar fraction. The interest of the data is based on their potential usefulness in the modelling of sulphation processes in film reactors. Data were measured from samples obtained in situ in a pilot scale falling film sulphation reactor.