(CNBC) — U.S. crude settled down at a six-year low of $43.88 a barrel after tumbling to $42.85 earlier in Monday’s session.

Brent oil fell nearly 3 percent on Monday and U.S. crude hit six-year lows on signs of higher output in the United States and Libya and a possible nuclear deal that could end sanctions for Iran, allowing more of its oil into the market.

A market data provider estimated a fresh build of more than 3 million barrels at the Cushing, Oklahoma delivery point for U.S. crude futures last week, traders said, adding to worries that stockpiles in the United States could hit record highs for a tenth straight week.

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