Abstract: Recent cosmological observations indicates that the present universe is undergoing an accelerated expansion. This acceleration of the universe a well established fact that is confirmed by various independent observational data including SNIa, CMB radiation etc. However this discovery can be maintained in general relativity by introducing a mysterious kind of energy source called the dark energy that can generate repulsive gravity [1, 2]. It is well known that perfect fluid with a constant equation of state (EOS) parameter lower than .