A gasdynamic model of the magnetosheath is extended into the tail region by incorporating a cometary tail field produced by mass loading. By means of test particle simulations, a picture of the martian pickup ion wake is described and contrasted with particle measurements of the Phobos 2 automatic space plasma experiment with a rotating analyzer (ASPERA). It is shown that the convection electric field alone is not sufficient to explain the observations. If magnetic shear stresses of the draped field are taken into account, the flux of low-energy oxygen ions close to the central wake of Mars (a persistent observational feature in the particle data) is reproduced. Simulation results suggest that the low-energy ion observations (E≤350 eV) of the ASPERA particle instrument are due to particles picked up in a source region at lower altitude close to the terminator plane at low latitudes, while moderate energy ions are created at high areographic latitudes, depending on the orientation of the transverse interplanetary magnetic field component. High-energy ions (E≥2 keV) usually originate from more distant regions in the magnetosheath or in the solar wind above the dayside of Mars. ¿ American Geophysical Union 1995