A bstract In this paper, we study cosmologies containing the reduced modified Chaplygin gas (RMCG) fluid which is reduced from the modified Chaplygin gas p = Aρ ? Bρ _( ?α )for the value of α = ?1 / 2. In this special case, dark cosmological models can be realized for different values of model parameter A . We investigate the viabilities of these dark cosmological models by discussing the evolutions of cosmological quantities and using the currently available cosmic observations. It is shown that the special RMCG model ( A = 0 or A = 1) which unifies the dark matter and dark energy should be abandoned. For A = 1 / 3, RMCG which unifies the dark energy and dark radiation is the favorite model according to the objective Akaike information criteria. In the case of A < 0, RMCG can achieve the features of the dynamical quintessence and phantom models, where the evolution of the universe is not sensitive to the variation of model parameters.
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