  The MiniBooNE experiment at Fermilab reports results from an analysis of
$\bar \nu_e$ appearance data from $11.27 \times 10^{20}$ protons on target in
antineutrino mode, an increase of approximately a factor of two over the
previously reported results. An event excess of $78.4 \pm 28.5$ events ($2.8
\sigma$) is observed in the energy range $200<E_\nu^{QE}<1250$ MeV. If
interpreted in a two-neutrino oscillation model,
$\bar{\nu}_{\mu}\rightarrow\bar{\nu}_e$, the best oscillation fit to the excess
has a probability of 66% while the background-only fit has a
$\chi^2$-probability of 0.5% relative to the best fit. The data are consistent
with antineutrino oscillations in the $0.01 < \Delta m^2 < 1.0$ eV$^2$ range
and have some overlap with the evidence for antineutrino oscillations from the
Liquid Scintillator Neutrino Detector (LSND). All of the major backgrounds are
constrained by in-situ event measurements so non-oscillation explanations would
need to invoke new anomalous background processes. The neutrino mode running
also shows an excess at low energy of $162.0 \pm 47.8$ events ($3.4 \sigma$)
but the energy distribution of the excess is marginally compatible with a
simple two neutrino oscillation formalism. Expanded models with several sterile
neutrinos can reduce the incompatibility by allowing for CP violating effects
between neutrino and antineutrino oscillations.
