Global crude oil prices jumped more than 4 percent, after a rally in equity markets and an unexpected fall in U.S. crude inventories. But worries over the health of the Chinese economy and a global oil glut kept the outlook uncertain.Brent crude oil futures was up 1.75 dollars, at 44.89 dollars a barrel. U.S. crude rose 1.60 dollars, at 40.20 dollars a barrel. Still, some analysts have lowered their forecast for Brent to 54 dollars a barrel in 2015, and 63 dollars a barrel in 2016.