China has no clear modus operandi in outbound energy deals. First came the ambush, as CNOOC leapt on Unocal. It then bagged various smaller targets in sudden attacks: the latest was Addax, a week ago. Now comes the pincer movement. CNPC, the parent of PetroChina, is trying to relieve Repsol of all or part of its 85 per cent holding in YPF, its Argentine unit that is worth potentially $17bn. All this while its smaller rival, CNOOC, is also sniffing around.

Neither bidder would be stretched by buying the whole thing. CNOOC, one-seventh the size of PetroChina by market capitalisation, could drop $20bn before its ratio of net debt to equity nudged over 30 per cent, the usual threshold for alarm. Repsol, meanwhile, has long been anxious to offload more of YPF than the 15 per cent it sold to a private Argentine investor two years ago. Weak gas prices, high oil export duties and erratic volumes have been a drag on the group for years. Freeing up capital to invest in higher-yielding upstream assets might narrow its persistent discount to European peers, on a price to cash flow basis.

YPF has been a persistent destroyer of value for the Spanish major ever since it paid $15bn for the company a decade ago. Even so, Repsol may not easily surrender control of an asset that now accounts for two-thirds of its output. And Buenos Aires wants as much as possible of YPF – producer of a third of the country's oil and a quarter of its gas – to find its way into Argentine hands. That implies pressure for a public share offering over a private deal.