times and behaves like a cosmological constant at late stage. This dual role is at the heart of the surprising properties of the GCG model. Moreover, the GCG model has been successfully confronted with various phenomenological tests involving SNe Ia data, CMB peak locations, gravitational lensing and other observational data [@gcgtest]. It is remarkable that the GCG equation of state has a well defined connection with string and brane theories [@gcgbrane], and this gas is the only gas known to admit a supersymmetric generalization [@susy].

In addition, it should be pointed out that the GCG model can be portrayed as a picture that cosmological constant type dark energy interacts with cold dark matter. However, since the equation of state of dark energy still cannot be determined exactly, the observational data show $w_X$ is in the range of $(-1.46, -0.78)$, the GCG model should naturally be generalized to accommodate any possible X-type dark energy with constant $w_X$. Therefore, we propose here a new generalized Chaplygin gas (NGCG) scenario as a scheme for unification of X-type dark energy and dark matter. The feature of this new model should also be exhibited in that dark sectors are uniformly described by an exotic background 