VIENNA, Dec. 20 (Xinhua) -- The weekly average prices of the Organization of Petroleum Exporting Countries (OPEC) continued to increase last week, reaching 88.39 U.S. dollars per barrel, the Vienna-based cartel said Monday.

OPEC weekly average prices increased for the third week. The first two weeks of this month, the OPEC weekly average oil price reached 84.90 and 87.80 dollars a barrel.

On the last five trading days, OPEC prices rose for four consecutive days.

However, the range of rise remained small, reaching a total increase of 0.82 dollars for five days, increasing from 87.96 dollars a barrel on Monday to 88.78 dollars a barrel on Friday.

Last week, in many areas of the United States and Europe it was the coldest in years, boosting the growth in demand for crude oil and heating oil.

However, better U.S. economic figures also pushed the dollar exchange rate up, which imposed pressure on oil prices. Meanwhile, tensions on the Korean Peninsula also increased the concerns of investors.

In the short term, the market was forecast to remain unchanged and international oil prices were expected to continue fluctuating.