Commodity prices mostly fell this week as traders balanced weak Chinese data against signs that the US Federal Reserve could curtail its quantitative easing stimulus policy sooner rather than later.

Fed Chairman Ben Bernanke told Congress on Wednesday that the US central bank could scale back stimulus measures soon if economic conditions improved.

But he said any tapering off could only happen once it had confidence that economic gains could be sustained, warning that a "premature tightening of monetary policy" could derail recovery in the United States, which is a key consumer of many commodities.

The US central bank has been on an aggressive $85 billion a month bond-purchase programme, or QE, as part of measures to boost growth.

OIL: Brent oil prices sank to a three-week low at $100.64 per barrel on Thursday on the back of poor Chinese economic data and Bernanke's comments.

Banking giant HSBC reported that manufacturing activity in China slowed in May for the first time in seven months, in a new sign of the weak recovery of the world's second-largest economy.

Its initial PMI for the month came in at 49.6, from a final 50.4 in April. A reading above 50 indicates growth and anything below points to contraction.

"Oil prices still find themselves on a downward trajectory," said Commerzbank analyst Carsten Fritsch.

"The price weakness was sparked by comments by Fed Chairman Bernanke and poor economic figures regarding China.

"Compounding this is an ample supply situation, as official US inventory data confirmed again."

Crude futures had fallen on Wednesday following the bearish US oil inventory report and Bernanke's testimony.

US gasoline demand was meanwhile expected to surge this weekend as the Memorial Day holiday Monday kicks off the summer vacation driving season.

By Friday on London's Intercontinental Exchange, Brent North Sea crude for delivery in July dropped to $102.27 a barrel compared with $104.47 a week earlier.

On the New York Mercantile Exchange, West Texas Intermediate (WTI) or light sweet crude for July sank to $93.91 a barrel from $95.64 for the expired June contract one week earlier.

PRECIOUS METALS: Gold hit one-month lows but rebounded into positive territory on Bernanke's remarks, and as dealers pushed cash into the safe-haven precious metal to shelter from volatile global stock markets.

"A poor end to the week for equities has helped gold recover $50 from its lows at the start of the week," said Tobias Morris, senior sales trader at CMC Markets UK.

"As traders assess whether the equity sell-off is a mere correction or the start of a longer retracement we have seen money returning to the yellow metal, with news yesterday that Ben Bernanke will continue with the stimulus plan until the economy improves helping to add support."

Silver meanwhile slid to $20.69, touching the lowest level since September 2010, before clawing back ground.

By late Friday on the London Bullion Market, the price of gold rose to $1,390.25 an ounce from $1,368.75 a week earlier.

Silver eased to $22.38 an ounce from $22.52.

On the London Platinum and Palladium Market, platinum fell to $1,455 an ounce from $1,470.

Palladium dipped to $729 an ounce from $736.

BASE METALS: Base or industrial metal prices mainly advanced in a choppy trading week.

"However, data showing the Chinese manufacturing sector having contracted in May do not bode well for future metals demand," noted Barclays analyst Gayle Berry.

By Friday on the London Metal Exchange (LME), copper for delivery in three months fell to $7,315.75 a tonne from $7,330 a week earlier.

Three-month aluminium slipped to $1,854.50 a tonne from $1,857.

Three-month lead rose to $2,055.75 a tonne from $2,008.

Three-month tin grew to $21,200 a tonne from $20,940.

Three-month nickel increased to $14,910 a tonne from $14,830.

Three-month zinc advanced to $1,861.75 a tonne from $1,841.

COCOA: The market drifted lower.

By Friday on LIFFE, London's futures exchange, cocoa for delivery in July eased to 1,528 pounds a tonne from 1,530 pounds a week earlier.

On New York's NYBOT-ICE exchange, cocoa for July dipped to $2,267 a tonne from $2,294.

COFFEE: Arabica prices struck the lowest level since March 2008 on expectations of abundant supplies from Brazil, dealers said.

"The plentiful supply is continuing to weigh on prices," said Commerzbank analysts in a research note to clients.

"The harvest has begun in Brazil and looks set to produce a record crop for a low-yield year."

By Friday on NYBOT-ICE, Arabica for delivery in July slid to 130.40 US cents a pound from 140.50 cents a week earlier.

On LIFFE, Robusta for July dropped to $1,978 a tonne from $2,042.

SUGAR: Prices slumped near to three-year lows, as the market continued to be plagued by expectations of large surpluses.

By Friday on NYBOT-ICE, the price of unrefined sugar for delivery in July dropped to 16.79 US cents a pound from 16.94 cents a week earlier.

On LIFFE, the price of a tonne of white sugar for August dipped to $475.50 from $477.90.

GRAINS AND SOYA: Soya advanced on the back of keen Chinese demand, while wheat and maize also registered gains.

"Soybeans are heading toward another weekly gain and its longest bullish run since February as the demand from China shows no signs of slowing down and reports that stockpiles are set to be at their lowest level since 2004," added Tobias Morris at CMC Markets UK.

By Friday on the Chicago Board of Trade, July-dated soyabean meal -- used in animal feed -- rose to $14.95 a bushel from $14.48 a week earlier.

Maize for delivery in July climbed to $6.57 a bushel from $6.52.

Wheat for July increased to $6.99 a bushel from $6.83.

RUBBER: Prices traded flat despite upbeat investor sentiment, dealers said.

The Malaysian Rubber Board's benchmark SMR20 ended at 246.00 US cents a kilo, down from 246.10 cents the previous week.