  We report on high angular resolution observations of the CO(7-6) line and
millimeter continuum in the host galaxy of the gravitationally lensed (z~2.8)
quasar RXJ0911.4+0551 using the Plateau de Bure Interferometer. Our CO
observations resolve the molecular disk of the source. Using a lens model based
on HST observations we fit source models to the observed visibilities. We
estimate a molecular disk radius of 1$\pm$0.2 kpc and an inclination of
69$\pm$6\deg, the continuum is more compact and is only marginally resolved by
our observations. The relatively low molecular gas mass, $Mgas=(2.3\pm
0.5)\times 10^{9}$ Msolar, and far infrared luminosity, $LFIR=(7.2\pm 1.5)
\times 10^{11}$ Lsolar, of this quasar could be explained by its relatively low
dynamical mass, $Mdyn=(3.9\pm 0.9)\times 10^9$ Msolar. It would be a
scaled-down version the QSOs usually found at high-z. The FIR and CO
luminosities lie on the correlation found for QSOs from low to high redshifts
and the gas-to-dust ratio ($45\pm 17$) is similar to the one measured in the
z=6.4 QSO, SDSS J1148+5251. Differential magnification affects the
continuum-to-line luminosity ratio, the line profile and possibly the spectral
energy distribution.
