The current‐voltage characteristics of cylindrical probes in a high velocity collisionless plasma flow have been investigated experimentally and theoretically. The plasma was generated by a focused laser pulse incident on a metallic target in vacuum, with an expansion velocityU, such thatkTi/Mi ≪ U2 < kTe/me. An analysis, developed from a stationary plasma analog to the flowing case, demonstrated a failure of plasma shielding of probe potential in the electron attracting region, even when&lgr;D = (kTe/4&pgr;nee2) 1/2 ≪ R, the probe radius. Under these conditions, modifications of relatively simple previous treatments were found to be valid for computing electron current to a probe. The electron characteristics derived from the present analysis agree well with experimental results for a voltage range of typically− 5 kTe /e < V < + 3kTe/earound plasma potential. The ion and electron portions of the characteristics are consistent with each other and with independent diagnostic measurements.