The weekly average price of the Organization of Petroleum Exporting Countries (OPEC) dropped to 108.05 U.S. dollars a barrel last week, the Vienna-based cartel said Monday.

The downgrade of Portugal's credit rating, which has increased the concerns about the European debt crisis, became the major factor suppressing the international oil prices last week.

During the five trading days last week, OPEC oil price decreased obviously on Monday from 109.12 dollars per barrel of the previous weekend to 107.74 dollars. On Tuesday, it rebounded to 108.34 dollars a barrel under the influence of such factors as profit-taking in the market.

Afterwards, OPEC oil price kept falling slightly, dropping to 107.73 dollars per barrel on Friday once again.

As the prospect of the European debt crisis remains not optimistic, and the U.S. economic growth remains uncertain as well, the investors worry that the weak world economy would be unable to support the growth in crude oil demand.

In addition, although the U.S. crude oil inventories last week fell by 6.22 million barrels due to the rising refinery utilization rates and the decreasing crude oil imports, its impact on the crude oil price was covered by the strength of the U.S. dollar exchange rate.

The U.S. exchange rate had reached its highest level for nearly seven weeks. The strong U.S. dollar increased the purchasing costs of crude oil, which offset the stimulation caused by the decrease in U.S. crude oil inventories.

According to analysts, for the next period, the demand for crude oil on the international oil market would remain relatively weak. The trend of the international oil prices would largely depend on the movement of the European debt crisis and the U.S. economic recovery progress.

At present, except to the arrival of peak oil consumption in the northern hemisphere in winter, there is no other significant factor to stimulate the oil market. It is expected that the international crude oil prices remain volatile in the near future.