Corrected: Oil prices fall for a second day on oversupply concerns

(The story Corrects time in second paragraph to 0041 GMT, not 0941 GMT.)

TOKYO (Reuters) - Oil fell edged lower on Tuesday, declining for a second day and sapping more strength from a third-quarter rally, amid signs that a global glut in crude may not be clearing as quickly as bulls had hoped.

U.S. crude was down 15 cents, or 0.3 percent, at $50.43 a barrel by 0041 GMT, after closing down $1.09 or 2.1 percent in the previous session.

The U.S. benchmark posted a third quarter gain of around 12 percent, its strongest quarterly gain since the second quarter of 2016, but has now dropped nearly 5 percent from a six-month high reached on Thursday.

Brent crude , the global benchmark, was down 18 cents, or 0.3 percent, at $55.94 a barrel. The contract fell 67 cents, or 1.2 percent, in the previous session.

Brent had notched a third-quarter gain of about 20 percent, the biggest increase for that quarter since 2004 and traded as high as $59.49 last week. It is down about 6 percent from that level.

Iraq said on Monday that exports rose slightly in September from its southern oilfields, while an earlier Reuters survey indicated that OPEC overall boosted output.

Oil prices climbed last week on tension in Iraqi Kurdistan after the region's independence vote, with Turkey threatening to close a pipeline that brings oil from the region in northern Iraq to the Mediterranean.

Turkey has not carried out the threat, analysts said.

The recent rally had also been driven by signs that a three-year crude glut is easing, helped by a production cut deal among global producers led by the Organization of the Petroleum Exporting Countries (OPEC).

However, Middle Eastern oil producers are concerned the price rise will stir U.S. shale producers into more drilling and push prices lower again. Key OPEC producers consider a price above $60 as encouraging too much shale output.

One bullish sign was a letter from Libya's National Oil Company on Monday that declared force majeure on deliveries from Sharara, the country's largest oilfield.

(Reporting by Aaron Sheldrick; Editing by Richard Pullin)