  The instanton approach to the in-gap fluctuation states is applied to the
spectrum of biased bilayer graphene. It is shown that the density of states
falls off with energy measured from the band-edge as $\nu(\epsilon)\propto
\exp(-|\epsilon/\epsilon_t|^{3/2})$, where the characteristic tail energy,
$\epsilon_t$, scales with the concentration of impurities, $n_i$, as
$n_i^{2/3}$. While the bare energy spectrum is characterized by two energies:
the bias-induced gap, $V$, and interlayer tunneling, $t_{\perp}$, the tail,
$\epsilon_t$, contains a {\it single} combination $V^{1/3}t_{\perp}^{2/3}$. We
show that the above expression for $\nu(\epsilon)$ in the tail actually applies
all the way down to the mid-gap.
