When the U.S Interior Department announced last week that it would walk back a decision to allow oil drilling in the Eastern Gulf of Mexico and along the Atlantic Coast, it drew the predictable praise from environmentalists and scorn from drilling advocates and business groups.

In a recent op-ed, Robert Sanchez of the James Madison Institute argues that those who supported the decision were ignoring the data. Sure, he writes, an oil spill could hurt Florida’s economy, but…

so could gasoline priced at $5 or more per gallon, and so could disruptions in oil supplies followed by long lines at the gas pumps. How many folks up North would take a chance on packing the kids in the family SUV and heading for Florida’s theme parks if they couldn’t be sure of refueling affordably (or at all) along the way?

Numbers based on 2006 MMS estimates of undiscovered technically recoverable resources. The central and western areas are already open to drilling.

“If Sen. [Bill] Nelson and others have their way, those vast energy deposits in the Gulf off Florida’s coasts will never be tapped,” he adds.

What he never mentions is how “vast” those energy deposits actually are. According to The Washington Post, Nelson was mystified by Obama’s original decision to open the eastern Gulf to drilling because that portion only contains 10 percent of the gulf’s overall oil deposits.

The data appears to support Nelson. The central and western portions, which are already open to drilling, respectively contain 30.3 and 10.7 billion barrels of undiscovered oil that can be extracted with existing technology, according to a 2006 report (.pdf) from the Minerals Management Service. The eastern gulf contains a mean estimate of 3.9 billion barrels.

By comparison, the United States imported more than 4 billion barrels of oil last year, according to the Energy Information Administration. Nearly half of that came from OPEC.

A study by the Collins Center for Public Policy, which examined the same Minerals Management report, concluded:

Aside from acknowledging the adage that every little bit helps, the development of oil and gas resources in both Florida’s state submerged lands and the federal waters in the Eastern Gulf of Mexico would have no discernible impact on the state’s or the country’s dependence on foreign oil.

Meanwhile, federal waters along the entire Atlantic seaboard contain a mean estimate of 3.82 billion barrels of oil. Roughly half of that supply lies in the North Atlantic, which was never part of Obama’s drilling plan (see this helpful map from the Post).

These estimates vary widely, in part because less is known about the areas where little drilling has occurred, but even the upper-bound estimates are less than those for the parts of the gulf where drilling is already allowed, post-spill moratoriums notwithstanding.