After eight brutal months on Wall Street, the Dow Jones industrial average finally made it official: Blue-chip stocks have stumbled into bear territory.

A brief 155-point slide on Friday afternoon brought the decline in the Dow to 20 percent from its October peak, an ignominious figure that is generally regarded as marking the start of a bear market. The index ended down 107 points, a mere 0.1 percent above the threshold. The broader Standard & Poor’s 500-stock index has not fallen quite as much.

The eight-month journey has roughly followed the twists of the subprime mortgage crisis, with a significant drop after the Bear Stearns collapse and a tantalizing rally when the economy appeared to recover slightly last month.

But in June, as the price of oil kept rising and the pain in the financial industry showed no signs of easing, the losses gained momentum. Many investors concluded that the economy was in worse shape than they had initially feared. This month, as the price of crude has gained about $13, the Dow has shed more than 1,000 points. The index closed at 11,346.51.