It is analysed, how the potential impact of large oil spills on seabird populations are dealt with in the strategic environmental impact assessments (EIA) of oil exploration in the Barents Sea (1988) and the Beaufort Sea (1996). Current knowledge on the effect of large oil spills on bird populations is reviewed as background information for the analysis. The analysis of the two EIA cases focus on what ecological science can deliver to the EIA process and how the EIAs can manage with what they get. The use of oil spill scenarios and impact indices in the EIA-reports is discussed.