Abstract: The invention relates to a process and a device for measuring the gelling of paraffin petroleum products, in particular, crude oil. The process involves: measuring, with respect to the temperature and over a given thickness, the propagation velocity and the amplitude of an ultrasonic wave in the crude oil being analysed; then determining the transition temperature T.sub.t, at which a sudden change in the thermal variation in the inverse of the propagation velocity is observed; determining the ratio of the slopes for the propagation velocity inverse obtained between the linear parts of the thermal variation of said propagation velocity, around said brake point corresponding to T.sub.t, above and below, respectively, the determined temperature T.sub.t ; determining the ultrasonic signal amplitude difference .DELTA.A between the temperature T.sub.t and a given lower reference temperature, for example T.sub.t -5.degree. C.