US petrol inventories sit at the highest level in decades for the start of summer driving season, threatening oil’s rally to $50 a barrel. More than 237m barrels of petrol was stocked away in tanks on June 17, the US Energy Information Administration reported Wednesday. That was 8.7 per cent more than a year before and the most for June in records dating back to the 1980s. This state of plenty is evident in New York’s gasoline futures market. In typical years, the contract for July delivery costs more than August. But after Wednesday’s report July gasoline was trading unchanged at $1.5929 per gallon, about a penny less than the August contract. This discount incentivises storing petrol rather than selling it to convenience stores. Petrol stocks remain inflated even though US drivers are shattering consumption records. In the week to June 17, the EIA estimated petrol demand at an all-time high 9.815m barrels per day, surpassing a previous peak set in 2007. A strengthening jobs market and cheap petrol prices have induced motorists to take to the roads for work and pleasure, while sales of fuel-efficient vehicles have slowed.