The golden age is over. Valero Energy rode an incredible wave over the past few years. Last summer, its shares hit about $78 – an almost eight-fold increase since 2003.

Now, with its stock at $51, North America’s largest oil refiner is considering selling about a quarter of its 3.1m barrels per day of capacity. Some of the proceeds could be invested overseas. Refining was long the least profitable part of the oil business, a result of excess capacity built in the 1970s. As rising demand tightened the market, so refining margins rose, expanding from less than $5 a barrel at the start of the decade to more than $30 in May 2007.