A substantial portion of the world's remaining oil and gas reserves are found in the Arctic. Exploration pressure will intensify as sea ice thinning and retreat continue, and the subsequent production could involve spills or blowouts under various kinds of sea ice. Existing models for the spread of oil under ice are inadequate because they are unable to replicate the complexity or uniqueness of different ice regimes. Through the novel combination of 3-D under-ice imagery from an autonomous under water vehicle (AUV) and oil-trajectory modelling we demonstrate that it is possible to overcome these deficiencies. Results suggest that we are presently underestimating the spread of oil under sea ice by an order of magnitude. This is an important result with wide ranging ramifications as it suggests that our present ability to contain and recover oil under ice is limited.