Recently, evaluation of GPS positioning accuracies has gained importance. Studies presented in this manner usually employ inter-station distances varying between 5 and 300 kin. In this study. the aim to assess GPS accuracies over longer baselines (i.e. on smaller or regional scales) ranging join 300 to 3000 kin. We adopted already published Least Squares functional models,for accuracy assessments and investigated the effects on long baseline solutions. We used GPS data from Scripps Orbit and Permanent Array Centre (SOPAC) archives. GPS data were processed using NASA's GIPSY OASIS II research software. Our results indicate that GPS positioning accuracies show dependency on both the observing session duration and inter-station distances over regional scales. New prediction formulas have: been derived for regional scales since accuracy estimation could riot be performed well with the ones that were previously derived We also noticed that the effect of inter-station distance appears to be significant only for baselines longer than 2000 km.