Undriven magnetic reconnection in a one-dimensional current sheet is investigated by means of a two-dimensional compressible and resistive Hall MHD (HMHD) code. Reconnection is set up by applying a spatially limited resistivity in the center of an isothermal Harris sheet. Although the magnetic fields on the two sides of the initial current sheet are equal and exactly antiparallel, both magnetic field and flow velocity components out of the simulation plane are self-consistently generated in the course of the reconnection process. The quasi steady state exhibits all features of Petschek-like reconnection, such as two pairs of shock waves attached to the diffusion region, a strongly converging flow toward the field line reversal region, and a weak fast mode expansion of the inflowing plasma. The reconnection rate measured in terms of the Alfv¿n Mach number well upstream of the diffusion region is within the analytic limits for compressible Petschek reconnection and slightly higher than in the corresponding MHD case. In contrast to MHD, the shock in HMHD is a subfast, strong (2→4), intermediate shock; the thickness is ≃10 ion inertial lengths, and the shocks exhibit an internal structure. The trailing left-handed slow mode wave train predicted from the integration of the stationary one-dimensional Hall MHD equations is not found. This is probably due to the fact that waves downstream of the shock are smeared out along the shock layer by the fast outflow jet. The shock waves generated during the decay of a current sheet are studied by a one-dimensional (1-D) Hall MHD simulation. In the 1-D case, the shocks are of slow mode type, and thus a left-handed intermediate mode wave train can form upstream of the shocks. The shock thickness is estimated to be at least a factor of 3 thicker than in 2-D HMHD fast reconnection. The intermediate shock in the 2-D HMHD simulation as well as the slow shock in the 1-D HMHD simulation exhibit an S-shaped hodogram. When starting the simulation from a quasi-steady Petschek state and subsequently allowing the resistivity to be spatially constant, a long and thin current sheet develops. Such a current sheet becomes unstable against the tearing mode.¿ 1997 American Geophysical Union