To determine separation distances between odour sources and residential areas to avoid odour nuisance and complaints by the residents, odour impact criteria OIC have to be adopted by the responsible authorities. There is a wide variety of OIC used for this purpose, which differ by the odour concentration threshold between 0.12 ou m(-3) and 10 ou m(-3) and by the tolerated exceedance probability of this threshold between 0.1% and about 35%. For two national OIC for a protection level of rural residential areas (Ireland with a threshold of 6 ou m(-3) and an exceedance probability of 2% and Germany 0.25 ou m(-3)/20%) and two national OIC fur urban residential areas (Ireland: 3 ou m(-3)/2%, Germany 0.25 ou m(-3)/13.6%), the direction depending separation distances were calculated, and the similarity to 166 various OIC was investigated. The large discrepancies among the national OIC provokes the question if separation distances calculated for the same protection level are then still comparable and thus meet general expectations or not. For this comparison the normalised mean standard error was selected as a statistical measure. There are two groups of OIC used in various jurisdictions: The first one with a low odour concentration threshold and a high exceedance probability evaluating ambient odour intensity close to the perception threshold (Germany) and the second group of the remaining countries with high odour intensity by using a high concentration threshold and a low exceedance probability. The direction depending separation distances of OIC with the same protection level can vary considerably. The OIC of the last group, evaluating higher ambient odour intensities, show a much lower sensitivity to site specific meteorological data. Therefore a higher exceedance probability seems more appropriate for the determination of OIC. Even if the similarity of separation distances by various OIC could be determined, the direction dependent separation distances differ considerably for the same protection level. (C) 2014 Elsevier Ltd. All rights reserved.