After an increase in prices for three consecutive weeks, the weekly average prices of the Organization of Petroleum Exporting Countries (OPEC) failed to reach above 80 U.S. dollars, falling to 78.13 dollars per barrel last week, the Vienna-based cartel said Monday.

According to figures published by OPEC, its oil prices reached a record high of 80.29 dollars last Monday, marking the highest level since Oct. 7, 2008.

Analysts believe that the drop of weekly average prices last week was caused by many factors.

The last report from the U.S. Energy Information Administration showed that its inventories of crude oil and refined oil stocks rose by 3.7 million barrels and 3.8 million barrels respectively. The crude oil prices therefore lost a strong support due to the relative abundance of inventory.

U.S. economic figures also played a part.

According to figures of the U.S. Labor Department, the number of initial claims for unemployment benefits increased by 11,000 last week. Economists previously forecast that there would be a reduction of 4,000.

Figures from the Commerce Department showed that U.S. retail sales saw a drop of 0.3 percent instead of an expected growth of 0.5 percent in December.

The disappointing figures of employment rate and retail sales raised concerns on the international oil market about recovery prospects of the American economy.