  XMM Newton observations of five high-luminosity radio-quiet QSOs (Q
0144-3938, UM 269, PG 1634+706, SBS 0909+532 and PG 1247+267) are presented.
Spectral energy distributions were calculated from the XMM-Newton EPIC
(European Photon Imaging Camera) and OM (Optical Monitor) data, with bolometric
luminosities estimated in the range from 7 x 10^45 to 2 x 10^48 erg s^-1 for
the sample, peaking in the UV. At least four of the QSOs show a similar soft
excess, which can be well modelled by either one or two blackbody components,
in addition to the hard X-ray power-law. The temperatures of these blackbodies
(~100-500 eV) are too high to be direct thermal emission from the accretion
disc, so Comptonization is suggested. Two populations of Comptonizing
electrons, with different temperatures, are needed to model the broad-band
spectrum. The hotter of these produces what is seen as the hard X-ray
power-law, while the cooler (~0.25-0.5 keV) population models the spectral
curvature at low energies. Only one of the QSOs shows evidence for an
absorption component, while three of the five show neutral iron emission. Of
these, PG 1247+267 seems to have a broad line (EW ~ 250 eV), with a strong,
associated reflection component (R ~ 2), measured out to 30 keV in the rest
frame of the QSO. Finally, it is concluded that the X-ray continuum shape of
AGN remains essentially constant over a wide range of black hole mass and
luminosity.
