Since 2003, worldwide oil prices have quadrupled and according to a new study, the price of oil is rising at a faster-than-exponential rate, and cannot be sustained.

In other words, we’re in the midst of an oil bubble, say researchers at ETH Zurich in Switzerland and East China University of Science and Technology in Shanghai, China.

Since it appears that the supply-demand balance has only a small effect on the price of oil, the researchers suggest that a major effect lies elsewhere. They point out several reasons why speculation, fed on rumors of rising oil scarcity, may be the positive feedback causing high oil prices. In addition, investors could be searching for a new high-return investment following the collapse of three recent economic bubbles in the US.