Doubts about the sustainability of the North American oil and gas boom center on rapidly declining output from many shale wells after they are drilled.
Shale skeptics point to the need to drill an ever-increasing number of new holes just to replace the declining output from existing wells, let alone expand production. At some point it will become impossible to keep up, they argue.
The problem has been likened to the Red Queen's Race in Lewis Carroll's "Through the Looking-Glass" where the chess piece warns Alice that "it takes all the running you can do, just to keep in the same place."