The Energy Information Administration (EIA), a branch of the Department of Energy, raised its estimate of the impact a moratorium on offshore deepwater oil drilling would have on US oil production, reports Reuters. The agency now says that the ban would curb oil output by 31,000 barrels per day (bpd) in the fourth quarter of this year and 82,000 bpd in 2011.

Last month the EIA forecast reductions of only 26,000 bpd for the fourth quarter and 70,000 bpd for next year.

While the moratorium would halt deepwater drilling, it would not stop deepwater oil production already under way. Though “drilling” is often used to refer to oil production in general, its meaning is technically restricted to drilling holes that search for oil. If a well is pumping oil, then “drilling” has concluded, and that well would be unaffected by the ban. The EIA’s lower forecast for US oil production reflects the moratorium’s impact on deepwater oil drilling projects that were expected to begin producing oil this year or the next.

Because the moratorium would postpone potential oil output, it would have an increasingly large impact on oil production as time wore on, said the EIA:

The reductions in crude oil production increase from a monthly average of about 10,000 bpd in September 2010 to nearly 100,000 bpd by December 2011.

That’s assuming the moratorium will even be in place. A federal court blocked the drilling ban in June, though the Obama administration is appealing the ruling. The administration may also counter with a new moratorium that could allow drilling in some deepwater fields.

Even if the US does lose 82,000 bpd of oil production on average in 2011, the EIA doesn’t think that will have an effect on prices. As Bloomberg reports, the EIA’s forecast for 2011 oil prices remains unchanged from last month’s forecast.

Part of the impact of delayed offshore drilling will be offset by greater oil production elsewhere in the US; though the EIA sees 82,000 fewer bpd coming from the Gulf, it expects total US production to fall by only 26,000 bpd—a small amount in comparison to the 5.37 million bpd that the EIA predicts the US will produce in 2011.