REFILE-COMMODITIES-Demand slump drives oil, base metals lower

* Weak demand, high stocks send commodities reeling

* Oil falls below $50; aluminium, copper weakest in 3 years

* Gold firms, safe haven appeals to investors

(Refiles to update session low in 3rd paragraph)

(Updates prices, quotes; changes dateline pvs SINGAPORE)

By Karen Foster

LONDON, Nov 20 (Reuters) - Crude oil and base metals extended their losses on Thursday, with oil falling for the fifth day running, and aluminium and copper at their weakest in three years as rising inventories underlined soft demand.

Oil fell below $50 a barrel, deepening losses over the previous four sessions as U.S. crude inventories climbed twice as much as expected, signalling an economic downturn is hitting hard and demand for fuel is falling. [O/R]