  The type Ia supernovae observational data are used to estimate the parameters
of a cosmological model with cold dark matter and the Chaplygin gas. The
Chaplygin gas model depends essentially on four parameters: the Hubble
constant, the velocity of the sound of the Chaplygin gas, the curvature of the
Universe and the fraction density of the Chaplygin gas and the cold dark
matter. The Bayesian parameter estimation yields $H_0 = 62.1^{+3.3}_{-3.4}
km/Mpc.s$, $\Omega_{k0} = -0.84^{+1.51}_{-1.23}$, $\Omega_{m0} =
0.0^{+0.82}_{-0.0}$, $% \Omega_{c0} = 1.40^{1.15}_{-1.16}$, $\bar{A} = c_s^2 =
0.93^{+0.07}_{-0.21} c $, $t_0 = 14.2^{+2.8}_{-1.3} Gy$ and $q_0 = -
0.98^{+1.02}_{-0.62}$. These and other results indicate that a Universe
completely dominated by the Chaplygin gas is favoured, at least as the type Ia
supernovae data are concerned. A closed and accelerating Universe is also
favoured. The Bayesian statistics indicates that the Chaplygin gas model is
more likely than the standard cosmological constant ($\Lambda CDM$) model at
55.3% confidence level when an integration on all free parameters is performed.
Assuming the spatially flat curvature, this percentage mounts to 65.3%. On the
other hand, if the density of dark matter is fixed at zero value, the Chaplygin
gas model becomes more preferred than the $\Lambda CDM$ model at 91.8%
confidence level. Finally, the hypothesis of flat Universe and baryonic matter
($\Omega_{b0}=0.04$) implies a Chaplygin gas model preferred over the $\Lambda
CDM$ at a confidence level of 99.4%.
