  Motivated by string/M-theory predictions that scalar field couplings with the
Gauss-Bonnet invariant, G, are essential in the appearance of non-singular
early time cosmologies, we discuss the viability of an interesting alternative
gravitational theory, namely, modified Gauss-Bonnet gravity, and present the
viability bounds arising from the energy conditions. In particular, we consider
a specific realistic form of f(G) analyzed in the literature that accounts for
the late-time cosmic acceleration and that has been found to cure the
finite-time future singularities present in the dark energy models, and further
examine the respective viability of the specific f(G) model imposed by the weak
energy condition.

General Relativity and Quantum Cosmology;Cosmology and Nongalactic Astrophysics;High Energy Physics - Theory