For Europe’s biggest energy companies, the oil-price rout has had one silver lining: Their little-loved refineries returned to churning out big profits. Now, that bright spot could be fading, even as oil prices slump. Analysts and executives are flagging the prospect of lower refining profits as summer gasoline consumption eases, lowering demand. The International Energy Agency, a Paris-based watchdog for the world’s biggest consuming countries, said earlier this month that “fissures are appearing” in the strong refining environment that has prevailed this year. Analysts don’t expect refining profits to crash in the same way oil prices have, at least in the near term. Major oil companies’ downstream businesses—including refining and the sale of petroleum products—will likely continue to perform better than they have for several years as weak prices for their key input and rising consumption bolster […]