  A simple analytical model for estimating the fraction (\Omega_{gas}) of
matter in gaseous form within the collapsed dark matter (DM) haloes is
presented. The model is developed using (i) the Press-Schechter formalism to
estimate the fraction of baryons in DM haloes, and (ii) the observational
estimates of the star formation rate at different redshifts. The prediction for
\Omega_{gas} from the model is in broad agreement with the observed abundance
of the damped Ly-\alpha systems. Furthermore, it can be used for estimating the
circular velocities of the collapsed haloes at different redshifts, which could
be compared with future observations.
