Oil down 3 percent, sinking for second day

U.S. crude futures tumbled 3 percent to lead the oil complex down for a second straight day on Tuesday as an investor flight to safe havens continued from worries of a Greece exit from the euro zone and China's deepening stock market losses.

Iran's determination to seal a nuclear deal with global powers to bring more of its crude to an oversupplied market and the restart of a key oil terminal in Libya also weighed on oil prices.

"The U.S. dollar and Treasuries are what people are buying right now," said David Thomson, executive vice-president at Powerhouse, an energy-specialized commodities broker in Washington.

U.S. crude was down $1.75, or 3.3 percent, to $50.78 by 10:19 a.m. EDT. It plunged 7 percent on Monday, its biggest percentage drop in a day since early February, and more downside momentum could push it to test the six-year low of $42.03 set in mid-March, technical analysts said.

Brent crude fell $1.12, or nearly 2 percent, to $55.42.