  A cosmological model with an exotic fluid is investigated. We show that the
equation of state of this ``modified Chaplygin'' gas can describe the current
accelerated expansion of the universe. We then reexpress it as FRW cosmological
model containing a scalar field $\phi$ and find its self--interacting
potential. Moreover motivated by recent works of Sen [sen1, sen2] and
Padmanbhan [pad] on tachyon field theory, a map for this exotic fluid as a
normal scalar field $\phi$ with Lagrangian ${\cal L}_{\phi} =
\frac{\dot{\phi}^2}{2} - U (\phi)$ to the tachyonic field $T$ with Lagrangian
${\cal L}_{T} = - V(T) \sqrt{1 - \dot{T}^2}$ is obtained.
