Israel’s unprecedented attack on Iran raises the specter of sharply higher gasoline prices, just as the summer driving season heats up.

That scenario now appears alarmingly close. On the evening of June 12th, Israel launched dozens of air strikes on Iranian military and nuclear sites. The attack threatens to inflame the Gulf, which pumps a third of the world’s oil. Brent crude, the global benchmark, rose by 8% on June 13th, to $74 a barrel (see chart). How high might it now go?