The monthly average crude oil prices of OPEC continued their fall and dropped to the lowest level in four months. The monthly average price fell to about 105 dollars a barrel last month, according to latest OPEC data on Tuesday. The fall of global crude oil prices is on the one hand the result of weak global demand and the bleak outlook for economic growth. On the other hand, the exploration of shale oil and the hike of US oil supply have both increased the expectation of more global oil supply. Insiders expect global oil prices may keep falling in the short-term.