World oil prices dipped briefly beneath 90 dollars a barrel Tuesday on growing economic gloom that was likely to further dampen demand for energy in the months ahead, traders said. OPEC on Tuesday cut its world oil demand growth forecast for 2008 to 1.02 percent from 1.17 percent previously, in the face of falling demand already occurring in the United States, the world's biggest consumer of energy. The price of crude oil has now plunged by almost 40 percent since striking record highs above 147 dollars per barrel in July.