We have compiled a catalogue of light curve solutions of contact binary stars. It contains the results of 159 light curve solutions. The properties of contact binary stars were studied using the catalogue data. As is well known since Lucy's (\cite{Lucy68a},b) and Mochnacki's (\cite{Mochnacki81}) studies, primary components transfer their own energy to the secondary star via the common envelope around the two stars. This transfer was parameterized by a transfer parameter (ratio of the observed and intrinsic luminosities of the primary star). We prove that this transfer parameter is a simple function of the mass and luminosity ratios. We introduced a new type of contact binary stars: H subtype systems which have a large mass ratio (q>0.72). These systems show behaviour in the luminosity ratio- transfer parameter diagram that is very different from that of other systems and according to our results the energy transfer rate is less efficient in them than in other types of contact binary stars. We also show that different types of contact binaries have well defined locations on the mass ratio - luminosity ratio diagram. Several contact binary systems do not follow Lucy's relation (L2/L1 = (M2/M1)0.92). No strict mass ratio - luminosity ratio relation of contact binary stars exists. Tables 2 and 3 are available in electronic form at http://www.edpsciences.org