  The supernova type Ia observational data are fitted using a model with cold
dark matter and the Chaplygin gas. The Chaplygin gas, which is characterized by
a negative pressure varying with the inverse of density, represents in this
model the dark energy responsible for the accelaration of the universe. The
fitting depends essentially on four parameters: the Hubble constant, the
velocity of sound of the Chaplygin gas and the fraction density of the
Chaplygin gas and the cold dark matter. The best fitting model is obtained with
H_0 = 65 km/Mpc.s, $c_s^2 \sim 0.92c$ and Omega_{c0} = 1, Omega_{m0} = 0, that
is, a universe completely dominated by the Chaplygin gas. This reinforces the
possibility that the Chaplygin gas may unify dark matter and dark energy, as it
has already been claimed in the literature.
