Since last July, the average oil prices of the Organization of Petroleum Exporting Countries (OPEC) have almost doubled, rising from less than 70 U.S. dollars per barrel (dpb) to over 140 dpb. Facing the skyrocketing prices, different people gave different reasons.

CONSUMING COUNTRIES: INADEQUATE SUPPLY MAIN FACTOR FOR PRICES HIKE

During the debates on why the oil prices surged so high, most Western oil consuming countries said the situation has largely resulted from supply shortage, and they blamed OPEC for refusing a production increase.

In the United States, the world's top energy consumer, the lower house of parliament has adopted a bill earlier this year which authorizes the U.S. government to sue OPEC for controlling oil prices.

In a report released recently by the International Energy Agency (IEA), it said that the real reason for the current high prices was the concerns on the global stable supply in the future.

IEA predicted an annual demand growth of 1.6 percent till 2013, which means the daily global oil output should rise from the current 86.87 million barrels to 94.14 million barrels.

IEA's latest energy report also adjusted its oil demand of the second half of this year from 86.10 million barrels per day to 86.90 million barrels, predicting even a daily demand of 87.70 million barrels for next year.