[macquire]

The concise Brittanica Encyclopedia estimates the surface of the Gulf of Mexico to be 1,550,000 km2 that is 1,550,000,000,000 m2 e maximum depth of the Gulf is 5203 m.
The average depth is somwhere between 0 and that value. I guess 1/4 the maximum depth (because it gave me an almost round number) of 1300 m. Multiplying 1,550,000,000,000 m2 x 1300m = 2.015 x 10 E 15 m3 or 5.3 X 10 E 17 USGallons (give or take 1223gallons) or about 650 Quadrillion gallons (650,000,000,000,000,000). The leak so far is 75,000 X 42 X 85 = 267,750,000 gallons or said another way, just 2.7 parts per 6,500,000,000 (six point five BILLION) .....Oil isn’t considered toxic until it reaches 10 parts per million.

[driftdiver]

Oil isn’t considered toxic until it reaches 10 parts per million.

Well I'm not an expert but these look toxic to me.

[combat_boots]

This answer I really like.

I’m not an engineer, but I do like your calculations.

Tnx.