This study examines a data set returned by IMP 8 and Geotail on January 29, 1995 during a substorm which resulted in the ejection of a plasmoid. The two spacecraft (s/c) were situated in the north lobe of the tail and both observed a traveling compression region (TCR). We show that in this instance dual s/c measurements can be used to model all three dimensions of the underlying plasmoid and to estimate its rate of expansion. For this event plasmoid dimensions of ΔX~18, ΔY~30, and ΔZ~10Re are determined from the IMP 8 and Geotail observations. Furthermore, a factor of ~2 increase in the amplitude of the TCR occurred in the 1.5 min it took to move from IMP 8 to Geotail. Modeled using conservation of magnetic flux, this increase in lobe compression implies that the underlying plasmoid was expanding at a rate of ~140 km/s. Finally, a reconfiguration of the lobe magnetic field followed plasmoid ejection which moved magnetic flux tubes into the wake behind the plasmoid where they would become available to feed the reconnection region. ¿ 1999 American Geophysical Union