The contribution presents the design of an original algorithm for the delimitation of service areas in a vector model of road network. Service areas are derived from the service network, computed for a selected centre on the basis of geometric network. The designed algorithm provides service areas that are delimited with positional accuracy higher than that of service areas computed by functions of three selected program tools (ArcView Network Analyst, Arc/Info Network and ArcGIS Network Analyst). Simultaneously, the contribution compares the service areas delimited by the designed algorithm with the service areas that were obtained using the mentioned program tools. By comparing the results of spatial analysis of service area delimitation, the algorithm designed by the authors and algorithms implemented in the tested tools are evaluated.