VIENNA, Jan. 2 (Xinhua) -- The Organization of Petroleum Exporting Countries (OPEC)'s weekly average crude oil prices went down by 1.51 U.S. dollars to 56.5 dollars per barrel last week, the cartel's secretariat said on Tuesday.

    There were only four trade days last week, from Tuesday to Friday. Except the drop from 57.45 dollars to 56.43 dollars on Wednesday, the daily oil prices fluctuated between 56.43 dollars and 56 dollars per barrel.

    During this long vacation of Christmas and the New Year, no specific price changes appeared last week.

    Iran's President Mahmoud Ahmadinejad kept insisting on protecting the right of using nuclear energy after the UN Security Council resolution on Dec. 23, which didn't influence the oil price much.

    OPEC wanted to keep the balance between supply and demand of the oil, according to the resolution of OPEC on Dec. 14.

    Experts said, the resolution actually showed the willingness of OPEC to maintain the oil prices at 60 U.S. dollars by cutting down the oil production.

    Weather forecast showed that the warm winter would proceed this week in the northeast part of the United States, which might have an impact on oil prices.