Some analysts and investors worry that oil companies will not spend enough either to sustain growth in their core businesses, or to open options in alternative energy sources for a world in which oil and gas consumption is constrained by climate policy or high prices.

OIL PRICES WTI, BRENT,1990 - 2014

Crude oil, natural gas futures end week lower

MARKETS: BoA says Saudi Arabia could be pushing for sustained weak crude oil prices

Cheaper oil 'no big threat' to Gulf economies, say analysts

North American shale-focused companies' financial performance has improved

World oil demand growth in 2014 is expected to reach 1.05 mb/d, following a downward revision of around 50 tb/d, mainly due to the weaker-than-expected performance of the OECD region.

Weakening global demand and increased Libyan oil exports contributed to a drop in the North Sea Brent crude oil spot price to an average of $102 per barrel (bbl) in August, $5/bbl lower than the July average and $10/bbl below the average in June.

MARKET WATCH: Crude oil futures end week lower

Lower oil price adds to economic pressure on Russia