Oh that reminds me of an incident with the council. We would service the tractors at the local depot as they travelled so slow, and we would have a 45 gallon oil drum to put the old engine oil in, and we would arrange when nearly full for it to be emptied, at one site we never seemed to need to empty the drum, then we had a visit by Shell I think it was, who has found on a farmers field oil oozing out of the ground, thinking it could be natural oil, the oil was tested, but that showed it was waste oil, he had not struck black gold, seems very small hole in drum and oil was leaking out that slowly we could not see there was a leak. The place where it leaked out was nearly 1/2 mile away.
Also had on the Falklands what seemed to be fuel oil grade oil, so all tanks tested for leaks, non found, so records checked, and it was found 9 months earlier there was a discrepancy, it would seem a delivery tanker had tried to put 6000 gallons in a nearly full tank, and it had over flowed, it took 9 months to come out and we were there for a good few months capturing the oil and putting it in tanks for disposal, likely burnt in the central heating boiler.
It seems there are some ships sank in the last war still allowing oil to be slowly released, however in the gulf war it was found there is bacteria that can eat oil, and the oil spilt was no where near as bad as expected to the environment.