Oil was headed for its biggest gain in nearly a month as oil supplies rose less than expected in the US and speculation built that the European Central Bank will cut interest rates.

Benchmark oil for June delivery rose $1.94 to $91.12 a barrel in afternoon trading on the New York Mercantile Exchange.

Oil rose as expectations mounted among investors for a rate cut next week from the ECB following another weak business survey in Germany.

The gains grew after the US Energy Department said crude oil supplies rose by 900,000 barrels, or 0.2%, to 388.6 million barrels last week. Analysts expected an increase of 1.4 million barrels.

A big decline in gasoline supplies was also positive for oil prices, indicating that demand picked up somewhat, although it was still down 1.7% over the four weeks ended April 19.

Brent crude, which is used to price oil used by many US refiners, rose $1.28 to $101.59 a barrel on the ICE futures exchange in London.