Latest data on US shale output indicates that production continues to rise. But it also shows that prices are rising and that efficiency is falling.

The EIA’s latest Drilling Productivity Report, released 15 May, indicates that output from the country’s key Permian shale formation is set to hit 2.421mn b/d in May and 2.492mn b/d in June, both record highs with the latter up 500,000 b/d on a year earlier.

The only solace for Opec is that the “new well oil production per...