The lack of volatility following the expiration of November traded options in London may have caused some traders to cover their short positions today, one dealer said.
"The options expiration in London may have freed up the market a little," the dealer said.
Copper for December delivery gained 1.45 cents at $1.8305 a lb, at the COMEX division of the New York Mercantile Exchange, its highest settlement since October 11. Trading ranged from $1.8090 to $1.8330.
Spot November ended the day up 0.60 cent at $1.9020 a lb, while back months closed 1.35 to 2.95 cents higher.
COMEX final copper volume was estimated at 14,000 lots, less than the 18,973 lots recorded on Tuesday.
"I didn't rally see anything in the news flow that was particularly favourable for copper today. There were a good number of rumours overnight on the SRB releases that don't look very bullish for the market," said one broker.
China's State Reserves Bureau is expected soon to sell about 80,000 tonnes of copper to the market, adding pressure to world prices near record highs, industry officials and traders said on Wednesday.
The latest estimate is higher than forecasts made last week between 30,000 and 50,000 tonnes, and the bureau responsible for managing China's strategic commodity stocks said it might eventually sell even more as it seeks to rein in high prices.
Meanwhile, copper warehouse stocks on the London Metal Exchange fell 125 tonnes to 64,900 tonnes on Wednesday. COMEX inventories were flat at 3,690 short tons in Tuesday's daily report.
Supporting the market's gains Wednesday was a weaker United States dollar against the euro as speculation grew that the European Central Bank would be much more hawkish at Thursday's monetary policy meeting.
In afternoon trade in New York, the euro was trading at $1.2070 from $1.2014 late Tuesday.
In other news, the head of the world's largest copper producer, Chile's Codelco, said Tuesday he expected the copper market to move into surplus in 2006.
Codelco CEO Juan Villarzu told Reuters in an interview that the copper surplus would grow to 300,000 tonnes in 2006, while cash copper prices would fall over the next three years to a more sustainable $2,200-2,400 a tonne.
London Metal Exchange three-months copper closed at $3,943 a tonne, up $38 from Tuesday's kerb close.