Judging from the crankish/alarmist tone of the quoted "engineer", I wouldn't really trust his evaluation. However, let's say that 1 gallon of oil actually does

Judging from the crankish/alarmist tone of the quoted "engineer", I wouldn't really trust his evaluation. However, let's say that 1 gallon of oil actually does poison a million gallons of water. A quick google search yields that there are approximately 346 quintillion gallons of water in the ocean. This means it would take about 346 trillion gallons of oil to poison the ocean. At a rate of 1 million gallons per week, this process would take about 6.6 million years. That is assuming that there are 346 trillion gallons of oil under the earth (good news for BP) and that the oil is never cleared or broken down once it enters the water.