  We use the Type Ia Supernova gold sample data of Riess {\it et al} in order
to constrain three models of dark energy. We study the Cardassian model, the
Dvali-Turner gravity modified model and the generalized Chaplygin gas model of
dark energy - dark matter unification. In our best fit analysis for these three
dark energy proposals we consider flat model and the non-flat model priors. We
also discuss the degeneracy of the models with the XCDM model through the
computation of the so-called jerk parameter.
