Brent crude oil hit an 18-month low of $91 per barrel on Thursday as the outlook for economic growth darkened, pointing to lower-than-expected energy consumption worldwide. China’s factory sector shrank for an eighth straight month in June as export order sentiment hit its weakest since early 2009, according to a survey indicating the country’s economic trough may extend well into the third quarter. The US Federal Reserve on Wednesday signalled a weaker outlook and disappointed some investors who had hoped for aggressive steps to boost the world’s top economy. Demand also looks shaky in the euro zone where borrowing costs have risen and the health of the banks has worsened. Brent crude oil futures for August fell $1.69 to a low of $91.00 per barrel, its weakest since December 2010, before recovering slightly to trade around $91.70 by 1040 GMT. Front-month US crude was down $0.80 at $80.65 per barrel, after earlier hitting an eight-month low of $79.92. “All very bearish” On top of the negative macro-economic news, oil was also hit by news on Wednesday of an unexpected rise in US crude inventories, which increased 2.86 million barrels, defying forecasts for a 1.1 million barrel decline, according to data from the US Energy Information Administration. Brent has so far fallen 10 percent this month and is now down almost 15 percent in 2012, despite a strong rally through the first two months of the year. It has slipped almost 30 percent from this year’s peak above $128 in March. Nearby Brent prices have fallen below forward futures for the first time in almost a year, pushing the front of the price curve into contango, a structure that is commonly associated with a weak and over-supplied market. Three years ago the Brent contango widened to the point where oil companies and trading houses could make money by buying crude oil, storing it at sea and then selling later. The US Federal Reserve did little to bolster financial markets on Wednesday. While Chairman Ben Bernanke said it was ready to do more to help recovery, many investors hoping for a third round of quantitative easing which would have boosted investment flows into assets like oil were disappointed. China’s export orders were at the weakest since early 2009, according to the HSBC Flash Purchasing Managers Index, the earliest monthly indicator of China’s industrial activity.