  We present the results of XMM-Newton observations of four AM CVn systems --
AM CVn, CR Boo, HP Lib and GP Com. Their light curves show very different
characteristics. The X-ray light curves show no coherent pulsations, suggesting
the accreting white dwarfs have relatively low magnetic field strengths. Their
spectra were best modelled using a multi-temperature emission model and a
strong UV component. We find that CR Boo and HP Lib have X-ray spectra with
abundances consistent with relatively low temperature CNO processed material,
while AM CVn and GP Com show an enhancement of nitrogen. A large fraction of
the accretion luminosity is emitted in the UV. We determine accretion
luminosities of ~1.6x10^{33} ergs/s and 1.7x10^{31} ergs/s for AM CVn and GP
Com respectively. Comparing the implied mass transfer rates with that derived
using model fits to optical and UV spectra, we find evidence that in the case
of AM CVn, we do not detect a significant proportion of the accretion energy.
This missing component could be lost in the form of a wind.
