Crude oil on the Nymex has slipped for the third consecutive day to US$84.9, while in London, crude dropped to US$84.83 after suffering losses for two days. The downturn has wiped off all the past gains triggered by economic optimism and a weak dollar. From among the many reasons pulling down oil prices, one is weak demand, another is a weak dollar in comparison to the euro. Oil prices tumbled even though stock markets rallied and the dollar fell compared to other major currencies. A weaker dollar usually props up oil prices since investors holding foreign currencies find they can buy more crude for the same price.