New York ? Wall Street rebounded smartly Friday, shooting higher as a surge in the dollar and another plunge in oil prices eased some of investors’ worries about losses at mortgage finance company Fannie Mae. The Dow Jones industrials soared more than 300 points, more than wiping out a big loss from the previous session, and all the major indexes had their best weekly gains since April.

The session extended a streak of volatility that has seen the Dow making frequent triple-digit moves as investors reacted feverishly to news about the financial sector, corporate earnings and the economy.

On Friday, the dollar, which has sagged along with the economy, reached its highest level against the euro since February, and in the process sent a wave of confidence through the stock market. And because the dollar’s strength has contributed to the recent skid in oil prices, light, sweet crude dropped sharply again, falling $4.82 a barrel to settle at $115.20 on the New York Mercantile Exchange. That brought crude’s decline over the past four weeks to more than $30.

Investors see the drop in oil as a big boost for the economy, because it should allow consumers to spend more freely. For the moment, that has allowed the market to set aside nervousness about the financial sector, which is still contending with the fallout from the year-old credit crisis.

Fresh financial worries surfaced Friday after Fannie Mae, the largest U.S. buyer and backer of home loans, reported a quarterly loss more than three larger than what Wall Street had expected and said it would slash its quarterly dividend to conserve cash.

Philip S. Dow, managing director of equity strategy at RBC Dain Rauscher in Minneapolis, said that while the strength in the dollar and the resulting drop in oil were attracting buyers Friday, Wall Street’s recent back-and-forth trading illustrates investors’ great anxiety.

“We live in a market where people react, they don’t anticipate,” he said. “So you’ve got this market that’s kind on a seesaw every day reacting to news.”

The Dow rose 302.89, or 2.65 percent, to 11,734.32. The blue chips fell nearly 225 points Thursday after concerns about the financial sector, a weak showing by retailers in July and a spike in weekly unemployment claims; Friday’s advance marked the seventh time in two weeks that the Dow rose or fell by triple digits.

Broader indicators also rose sharply Friday. The Standard & Poor’s 500 index advanced 30.25, or 2.39 percent, to 1,296.32 and the Nasdaq composite index advanced 58.37, or 2.48 percent, to 2,414.10.

For the week, the Dow rose 3.6 percent, the S&P gained 2.9 percent and the technology-heavy Nasdaq jumped 4.5 percent.