Crude oil rose to a record above $143 a barrel on speculation the dispute over Iran's nuclear program may disrupt supply from OPEC's second largest producer.

Pressure on Iran to end its uranium enrichment program and the falling value of the US dollar may drive prices to $170 a barrel, OPEC President Chakib Khelil said recently. Oil is headed for its biggest six-month gain since 1999 as investors shun equities for commodities, looking for a hedge against a weaker dollar and rising inflation.

"Tensions ratchet up in Iran and troubles continue in Nigeria, drawing funds into the market," Robert Montefusco, a broker at Sucden (UK) Ltd in London, said. "The weak dollar is also helping. The market does not want to break down just yet."