**Abstract**

In traditional oil spill risk assessments, the mortality of seabirds is typically assessed based on a simulated amount of oil combined with a statistical and static (seasonal mean) number of birds within a given grid cell. The size of the cell is typically in the order of 10 by 10 km. Cell averaging in a coarse Eulerian grid will inevitably introduce a high degree of uncertainty with respect to real impact, and due to the patchiness in seabird distribution may result in over-estimation of impacts outside high-density areas and underestimation within high-density patches. Lagrangian agent-based modelling of species movements and oil drift directly would provide consistent results independent of the grid resolution and, at the same time, provide a fine-scale resolution of potential impacts. The robustness of this approach is demonstrated for a potential oil spill in the Barents Sea in an area with a high density of Common Guillemot, followed by a discussion on how this approach can improve future risk assessments during oil spills.

**Keywords:** oil spill risk assessments, common guillemot, Barents Sea, agent-based modelling, Langrangian modelling
