In magnetospheric plasmas it is possible for plasma gradients to cause error in electric field measurements made by satellite double probes. The space charge enhanced plasma gradient induced error is discussed in general terms, the results of a laboratory experiment designed to illustrate this error are presented, and a simple expression that quantifies this error in a form that is readily applicable to satellite data is derived. The simple expression indicates that for a given probe bias current there is less error for cylindrical probes than for spherical probes. The expression also suggests that for Viking data the error is negligible. ¿ American Geophysical Union 1994