  A cosmological model with a new variant of Chaplygin gas obeying an equation
of state(EoS), $P = A\rho - \frac{B}{\rho^{\alpha}}$ where $B= B_{0}a^{n}$ is
investigated in the context of its thermodynamical behaviour. Here $B_{0}$ and
$n$ are constants and $a$ is the scale factor. We show that the equation of
state of this `Variable Modified Chaplygin gas' (VMCG) can describe the current
accelerated expansion of the universe. Following standard thermodynamical
criteria we mainly discuss the classical thermodynamical stability of the model
and find that the new parameter, $n$ introduced in VMCG plays a crucial role in
determining the stability considerations and should always be \emph{negative.}
We further observe that although the earlier model of Lu explains many of the
current observational findings of different probes it fails the desirable tests
of thermodynamical stability. We also note that for $n < 0$ our model points to
a phantom type of expansion which, however, is found to be compatible with
current SNe Ia observations and CMB anisotropy measurements. Further the third
law of thermodynamics is obeyed in our case. Our model is very general in the
sense that many of earlier works in this field may be obtained as a special
case of our solution. An interesting point to note is that the model also
apparently suggests a smooth transition from the big bang to the big rip in its
whole evaluation process.
