For drilling companies the more upstream spending the better, surely? So warnings from the CEO of the biggest, Schlumberger, of overheating in US shale should be taken seriously.

Recent growth in US shale output, particularly in Texas’ Permian Basin is unsustainable, driven by “US equity investors who are encouraging, enabling and rewarding short-term production growth in spite of marginal project economics,” says Paal Kibsgaard, CEO of global number one oil services firm...