© Reuters. A worker fills a tank with subsidized fuel at a fuel station in Jakarta By Henning Gloystein SINGAPORE (Reuters) - A slump in oil below $50 a barrel - a level it has held above for most of the past decade - has raised the prospect of a new era of lower prices, although a return to super-cheap oil seems unlikely. Prices below $50 for the two crude oil benchmarks, North Sea Brent and U.S. West Texas Intermediate (WTI) , were the norm prior to 2005. Brent averaged just $18.37 a barrel in the 1990s, WTI $19.70 a barrel, and both only broke above $50 for the first time in late 2004. China's explosive economic growth over the past decade, coupled with flatlining global output, saw Brent soar above $140 in 2008 and it has spent more than 90 percent of the past decade above the $50 mark. But producers globally, in... More