The sector structure of the interplanetary magnetic field and the solar wind velocity at the sector boundaries have been compared at two widely separated locations. Magnetic field and solar wind velocity observations made aboard Mariner 5 en route to Venus and with the near-earth satellites Explorer 33, 34, and 35 have been compared at separations of up to 0.3 AU, 50¿ in heliocentric longitude and 7¿ in heliographic latitude. The polarity pattern of the magnetic sectors was found to be very similar at the two locations, and 18 pairs of corresponding sector boundaries were identified. These sector boundaries were used to identify corresponding portions of the solar wind at each spacecraft so that their velocities could be compared. One-hour averages of the velocities in the vicinity of the sector boundaries showed the velocities to be systematically different. The velocities at earth exceeded those at Mariner 5 by as much as 30% (or 120 km/s). Instrumental effects and measurement errors were considered but rejected as potential causes of the velocity differences. Temporal variations of the solar source of the plasma and an overall radial acceleration of the solar wind were also rejected on both theoretical and observational grounds. The most plausible explanations of the observed velocity differences are (1) a preferential acceleration of sector boundaries with distance, perhaps caused by stream-stream interactions: or (2) a dependence of the solar wind velocity on heliographic latitude. The second explanation is consistent with the evidence of a possible latitude dependence in the solar wind velocity inferred from an analysis of Vela satellite data by Hundhausen et al. (1971). Both sets of data imply a gradient of ?10 km/s per degree of latitude.