Dislocation modelling is used to examine the GPS velocity vectors for the Marmara Sea region. First, the vectors due to the known Anatolia/Eurasia rotation are reproduced by introducing structures that approximate the large-scale tectonics. Observed features of the smaller scale fault system in the Marmara region are then progressively included with slip amplitudes and directions adjusted to fit an 80-vector subset of the GPS data. The motion in the Marmara Sea region is partitioned with the faults that bound the north of the basin carrying more strike-slip motion than predicted from the Anatolia-Eurasia plate motion and faults to the south having a greater perpendicular component. Taken together however, there is no net opening across the Marmara Sea perpendicular to the overall trend of the boundary and thus deformation in the Marmara region results only from the pull-apart geometry of the North Anatolian fault. No extension related to the Aegean system is needed to explain the observations. The GPS results are consistent with motion over the last 5 Myr that has been determined from geological reconstructions.