The war at sea took a huge toll during WW2. Has there been an official estimate of how much oil was spilled into the oceans during the world wide conflict?
I found a paper from 2005 analyzing the current sate of potentially polluting wrecks from World War 2. It has the information we need:
A low estimate would be 1.5 billion gallons (assuming 20 percent full at time of wreck). A reasonable average would be 3.8 billion gallons of oil spilled in maritime waters during World War 2. This estimate includes both military vessels and non-military vessels sunk during World War 2. It does not include oil spilled in rivers or freshwater lakes.