... but how do we put that cost into perspective?
The oil rig spill in the Gulf of Mexico has been compared to the Exxon Valdez disaster in Prince William Sound in Alaska in 1989 which dumped 10.8 million gallons of oil into an enclosed area. Though it makes an easy sound bite, I don't think it's a good comparison on several levals.
Prince William Sound is an area enclosed by islands and about 15,000 square miles in area. The Gulf of Mexico comprises an area of roughly 615,000 square miles or more than 40 times larger and flushed by the Gulf Stream providing a global scale.
In trying to find a better comparison it occurred to me that the oil from torpedoed tankers in the gulf of Mexico during the Second World War might provide some insight.
During the period from December 7, 1941 to May 8, 1945 (VE Day), 1,244 days, I found the following:
Ships torpedoed in The Gulf of Mexico - total of 46, of which 27 were oil tankers.
Based on the average oil tanker of the period having a capacity of 16,613 long tons (2,240 pounds per long ton) and a gallon of oil weighing about 7 pounds ---
That means during that 1,244 day period roughly 143,536,320 gallons of crude oil were dumped into the Gulf or about 115,383 gallons per day, to wash up on Gulf shore beaches. (More if you consider the fuel load on the other merchant ships sunk during that period... but not that much more.)
The current oil spill has, according to the news, has an output of about 5,000 barrels per day. Multiply that times 55 gallons per barrel and you get 225k gallons per day versus the 115.3k brought by all out, unrestricted submarine warfare.
Is it bad? It's probably worst that you think.