  We study a generalized version of Chaplygin gas as unified model of dark
matter and dark energy. Using realistic theoretical models and the currently
available observational data from the age of the universe, the expansion
history based on the type Ia supernovae, the matter power spectrum, the cosmic
microwave background radiation anisotropy power spectra, and the perturbation
growth factor we put the unified model under observational test. As the model
has only two free parameters in the flat Friedmann background [$\Lambda$CDM
(cold dark matter) model has only one free parameter] we show that the model is
already tightly constrained by currently available observations. The only
parameter space extremely close to the $\Lambda$CDM model is allowed in this
unified model.
