  We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star
that gave rise to the microlensing event OGLE-2011-BLG-0265. Such a system is
very rare among known planetary systems and thus the discovery is important for
theoretical studies of planetary formation and evolution. High-cadence temporal
coverage of the planetary signal combined with extended observations throughout
the event allows us to accurately model the observed light curve. The final
microlensing solution remains, however, degenerate yielding two possible
configurations of the planet and the host star. In the case of the preferred
solution, the mass of the planet is $M_{\rm p} = 0.9\pm 0.3\ M_{\rm J}$, and
the planet is orbiting a star with a mass $M = 0.22\pm 0.06\ M_\odot$. The
second possible configuration (2$\sigma$ away) consists of a planet with
$M_{\rm p}=0.6\pm 0.3\ M_{\rm J}$ and host star with $M=0.14\pm 0.06\ M_\odot$.
The system is located in the Galactic disk 3 -- 4 kpc towards the Galactic
bulge. In both cases, with an orbit size of 1.5 -- 2.0 AU, the planet is a
"cold Jupiter" -- located well beyond the "snow line" of the host star.
Currently available data make the secure selection of the correct solution
difficult, but there are prospects for lifting the degeneracy with additional
follow-up observations in the future, when the lens and source star separate.
