  In this paper, we carry out a study of viable cosmological models in
$f(R)$-gravity at the background level. We use observable parameters like
$\Omega$ and $\gamma$ to form autonomous system of equations and show that the
models under consideration exhibit two different regimes in their time
evolution, namely, a phantom phase followed by a quintessence like behavior. We
employ statefinder parameters to emphasize a characteristic discriminative
signature of these models.
