Regulators in the US and the UK risk distorting the world’s two largest oil markets if they do not agree the same rules for speculators, the International Energy Agency, the western countries’ oil watchdog, warned.

“Harmonised international norms would minimise migration of trades between exchanges or to less regulated platforms,” the IEA said on Wednesday. “Energy markets in the US and the UK are inextricably linked through look-alike contracts and arbitrage.”