Patricia Minczeski

No single factor can completely explain this summer’s surprising market moves. But one can help: so-called real yields. Real yields are what you get on U.S. government bonds after compensating for inflation, and are typically associated with the yields on Treasury inflation protected securities, or TIPS. Right now those aren’t just low, they are negative.

Traders are betting on fresh upheaval in the oil market, in an abrupt turnaround from the calm of recent months. U.S. oil prices have slid 12% since the end of August, and on Tuesday notched their biggest one-day drop since June. Though the market has clawed back some of those declines, many say trading in the options market shows investors preparing for further drops, as pressures on crude prices mount from forces including a slow recovery in fuel demand and the presidential election. ...

When Laura and Marco barreled toward Louisiana and Texas this week, companies closed more than four-fifths of offshore oil production in the Gulf of Mexico to protect equipment and personnel. Crude-oil prices barely budged. The insouciance was symptomatic of an exceptionally subdued summer in the market. After convulsing this winter and spring,...