A trio of closely watched energy organizations all raised their forecasts for American oil production this week, but the prognosticators can't seem to agree on one thing: Just how much more crude will U.S. drillers pump?

The flexibility and innovation in the U.S. shale oil patch — where new production can be started up quickly — is making it difficult for forecasters to make projections about American oil supply in 2018, the Paris-based International Energy Agency said in a monthly report on Thursday.

That might explain why forecasts this week were all over the map.

The U.S. Energy Information Administration on Tuesday said it expects U.S. output to grow by 780,000 barrels a day next year. The following day, the 14-member oil cartel OPEC forecast growth of 1.05 million barrels a day. And on Thursday, IEA said it sees the American oil patch raising output by 870,000 barrels a day.

"That's a wide margin of error, so the key takeaway is no one really knows what that value is going to be, but it is going to be a sizable chunk," Matt Smith, director of commodity research at ClipperData, told CNBC's "Squawk Box" on Thursday.