We present the XMM-Newton X-ray eclipse lightcurve of the dwarf nova OY Car .
The eclipse ingress and egress are well resolved for the first time in any dwarf nova placing strong constraints on the size and location of the X-ray emitting region .
We find good fits to a simple linear eclipse model , giving ingress/egress durations of 30 \pm 3 s ( \Delta \phi _ { orb } = 0.0055 \pm 0.0006 ) .
Remarkably this is shorter than the ingress/egress duration of the sharp eclipse in the optical as measured by ? and ascribed to the white dwarf ( 43 \pm 2 s ) .
We also find that the X-ray eclipse is narrower than the optical eclipse by 14 \pm 2 s , which is precisely the difference required to align the second and third contact points of the X-ray and optical eclipses .
We discuss these results and conclude that X-ray emission in OY Car most likely arises from the polar regions of the white dwarf .

Our data were originally reported by ? , but they did not make a quantitative measurement of eclipse parameters .
We have also corrected important timing anomalies present in the data available at that time .