[whd23]

Lessee... 4 billion barrels at 55 gallons/barrel * 8 lbs per gallon = 880 million tons.

So apparently we can get greater than 100% mass efficiency on this miracle process.....

The numbers still don't work, but you used the density of water, not oil. Oil is lighter than water (it floats). Petroleum oil has an density of only approximatly 82.2% of water.

[whd23]

Whoops! I missed the following post that pointed out that a barrel of oil is only 42 gallons. So:
(4x10^9 barrels) * (42 gallons/barrel) * (6.58 lbs/gallon) / (2000 lbs/ton) = 552.7x10^6 tons.

Looks close enough for me!