NEW YORK, Sept. 26 -- For three straight days, selling pressure had been building on the Street, rooted in something Wall Street could do nothing about: a waterway six thousand miles away that carries roughly twenty percent of the world's seaborne oil through a twenty-one-mile channel. Thursday changed the math, at least for one afternoon.

Iran's foreign minister Abbas Araghchi, speaking at the sidelines of the United Nations General Assembly in New York, told reporters his government could reopen the Strait of Hormuz within seven days, contingent on the United States lifting its naval blockade and releasing $12 billion in frozen Iranian assets. Whether Washington was serious about either condition, or whether Tehran was, remained unclea...