HOUSTON — Oil prices tumbled below $50 a barrel on Monday, spooking global financial markets and signaling that the remarkable 50 percent price drop since June was continuing this year and even quickening.

The new drop in American and global benchmarks of more than 5 percent was accompanied by reports of increased Middle Eastern oil exports, continuing increases in American production and renewed worries about the declining economic fortunes of Europe.

The plunge once again sent fear through global markets. The Standard & Poor’s 500-stock index fell 37.62 points, or 1.83 percent, to 2,020.58. The Vix, a measure of market volatility that is known as Wall Street’s fear gauge, leaped about 12 percent. And in Tokyo, the Nikkei 225 tumbled more than 2.5 percent Tuesday in morning trading.

In response, investors sought safety in government bonds around the world. As bond prices rose, the yield on the 10-year Treasury note fell to 2.03 percent on Monday.