  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 (1968a,b) and Mochnacki's (1981) 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. We also show that different
types of contact binaries have well defined locations on the mass ratio -
luminosity ratio diagram. All contact binary systems do not follow Lucy's
relation ($L_2/L_1 = (M_2/M_1)^{0.92}$). No strict mass ratio - luminosity
ratio relation of contact binary stars exists.
