In Slovenia one parametrical volume functions, adapted uniform French (AUF) tariffs, are used in order to determine stands growing stock. The purpose of the dissertation is to establish the reliability of tariffs for estimating stands growing stock and to investigate the possibilities of their improvementwith stratification. On the basis of true tree volume estimates (vn), calculated by means of section measurements (Newton method) regional three parametrical (diameter (d), tree height (h), diameter at 7 m tree height(d7)), regional two parametrical (d and h), and local one parametrical (d) volume functions (tariffs) were created for the tree species of spruce, fir and beech. The reliability of the functions was also tested. Trees at sampling plots in two forest units were measured in terms of dendrometric parameters d, h, d7 and later reference tree volumes (vr) were calculated by means of regional three parametric volume functions. The influence of site condition, developmental stage, tree species and height class on the reliability of tree volume estimate was analyzed. From reference tree volumes regional two parametrical volume functions (d and h) were calculated for both locations and all three tree species. They were further used to calculate regional reference tree volumes (vrr) and local tariffs (d) for individual strata (tree species, developmental stage, site). The reliability of three tariff application methods (existing, optimally selected and local tariffs) was examined. According to the existing AUF tariffs the mean tree volume estimate deviates from the reference by -5.7 % on average (from -16.7 to 19.5 %). According to the optimally selected AUF tariffs the mean tree volume estimate deviates from the reference by 0.1 % on average (from -0.8 to 2.2 %).On the other hand the mean tree volume estimate according to the local tariffs deviates from the reference by -0.1 % on average (from -0.3 to 0.2 %).Tariffs are therefore reliable enough for calculating growing stock estimates if they are suitably selected for a homogenous site stratum. The existing estimate of biomass quantity is unreliable due to its grounds in unreliable growing stock estimates and unconfirmed conversion/expansion factors.