A method is disclosed for the treatment of a liquid, in particular a mineral oil, for increasing the portion of low-boiling fractions. The treatment comprises generating pressure waves having a first frequency, subjecting the liquid to said pressure waves in a region of application and feeding the so-treated liquid to a tank. At least one pipe flowed through by the treated liquid and immediately following said region of application is excited to oscillations of a second frequency, which is the resonance frequency of the excited system.