The effectiveness of bioremediation for oil spills has been difficult to establish on dynamic, heterogeneous marine shorelines. A new interpretative technique used following the 1989 Exxon Valdez spill in Alaska shows that fertilizer applications significantly increased rates of oil biodegradation. Biodegradation rates depended mainly on the concentration of nitrogen within the shoreline, the oil loading, and the extent to which natural biodegradation had already taken place. The results suggest ways to improve the effectiveness of bioremediation measures in the future.