Concerns over slower global economic growth sent oil prices down for another time this week. Brent crude oil futures LCOc1 were down at $71.38 per barrel. U.S. West Texas Intermediate (WTI) crude futures CLc1 dropped to $65.42 a barrel. Data released on Wednesday showed crude oil output rose by 100,000 barrels per day to 10.9 million bpd in the week ending Aug 10.