How many gallons of water are in gulf of Mexico?

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...

About 200,000 gallons per day so that would mean about 3,600,000

1000000 gallons 10^6

2,434,000,000,000,000 (2.434 quadrillion) cubic meters, or 2.434 million cubic kilometers.

264.172 gallons.