The amount of oat grain yield and its components were analysed on the basis of data from field experiments carried out in 1981-1997 in four regions diversified as to soil and precipitation conditions. High grain yield was obtained under medium soil and good precipitation conditions (upland region), which points to their interaction in determining oat productivity. At these environmental conditions the yield and its components were relatively little variable (CV = from 5.8 to 13.8%). On light soils and with insufficient precipitation grain yield was the lowest (2.5 t/ha). However, it remained on the same level as yield from the mountain areas where the amount of precipitation was twice higher. This reveals very good adaptation of this species to unfavourable environment conditions. The percentage of individual components in yield formation was estimated using multiple regression method. Under favourable environment conditions oat grain yield was determined mainly by the number of panicles per m² (89% for series B). On weak (sandy) soils grain yield was determined by a number of grains per panicle (82,5% for series D), whereas in the mountain area grain yield was determined by all components.