  Let $G^\sigma$ be an orientation of a simple graph $G$. In this paper, the
permanental polynomial of an oriented graph $G^\sigma$ is introduced. The
coefficients of the permanental polynomial of $G^\sigma$ are interpreted in
terms of the graph structure of $G^\sigma$, and it is proved that all
orientations $G^\sigma$ of $G$ have the same permanental polynomial if and only
if $G$ has no even cycles. Furthermore, the roots of the permanental polynomial
of $G^\sigma$ are studied.
