  The RENO experiment has observed the disappearance of reactor electron
antineutrinos, consistent with neutrino oscillations, with a significance of
4.9 standard deviations. Antineutrinos from six 2.8 GW$_{th}$ reactors at the
Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors
located at 294 m and 1383 m, respectively, from the reactor array center. In
the 229 day data-taking period between 11 August 2011 and 26 March 2012, the
far (near) detector observed 17102 (154088) electron antineutrino candidate
events with a background fraction of 5.5% (2.7%). The ratio of observed to
expected numbers of antineutrinos in the far detector is $0.920 \pm 0.009({\rm
stat.}) \pm 0.014({\rm syst.})$. From this deficit, we determine $\sin^2 2
\theta_{13} = 0.113 \pm 0.013({\rm stat.}) \pm 0.019({\rm syst.})$ based on a
rate-only analysis.
