A catalogue of light curve solutions of contact binary stars has been compiled. It contains the results of 159 light curve solutions. Properties of contact binary stars were studied by using the catalogue data. As it is well known since Lucy's (1968ApJ...151.1123L, 1968ApJ...153..877L) and Mochnacki's (1981ApJ...245..650M) works, 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 proved that this transfer parameter is a simple function of the mass and luminosity ratio. This newly found relation is valid for all systems except H type systems which have a different relation. We introduced a new type of contact binary stars: H subtype systems which have a large mass ratio (q>0.72). These systems show highly different behaviour on the luminosity ratio - transfer parameter diagram from other systems and according to our results the energy transfer rate is less efficient in them than in other type of contact binary stars. (5 data files).