NEW YORK (AFP) - Petroleum-linked shares rallied on Tuesday, lifting the Dow and S&P 500 after US oil prices closed above US$50 a barrel for the first time since July.

Dow members Chevron and ExxonMobil climbed 2.2 per cent and 1.6 per cent as supply disruptions in Nigeria propelled the oil market to fresh multi-month highs.

But the Nasdaq finished modestly lower after two biotech companies, Biogen and Alexion Pharmaceuticals, reported disappointing clinical results on treatments to address multiple sclerosis and a neuromuscular disease called MG, respectively.

Biogen slumped 12.8 per cent and Alexion 10.9 per cent.

At the closing bell, the Dow Jones Industrial Average was at 17,942.25, up 0.1 per cent.

The broad-based S&P 500 rose 0.1 per cent to 2,112.37, while the tech-rich Nasdaq Composite Index shed 0.1 per cent to 4,962.40.