A broadband method for measuring the dielectric constant of liquids is presented. The method utilises both an automatic network analyser and a computer. It is based upon measurements of resonance frequencies andQ-factors in resonators filled with the liquid. First the physical shape and the calculation model are described, then practical measurements of unrefined oil from the North Sea are presented. They show that the relative real part of the dielectric constant drops from approximately 2.17 to 2.15 and that the relative imaginary part falls from about 40 × 10−3to 9 × 10−3in the frequency range 300 MHz – 12 GHz.