How much oil was spilled in the 2010 BP oil spill in the Gulf of Mexico?

Answer:

An estimated 100 million to 210 million gallons of crude oil have leaked into the Gulf as of 2010 July 19.

This is also equivalent to about:
300,000 - 600,000 tonnes.
2 million - 4 million barrels.
340 million to 650 million litres.