Crude oil prices drifted further into negative territory Thursday amid continued signs of sluggish sector and general economic growth.

Brent crude oil prices lost about a half percent from the previous close in early Thursday trading to sell for $63.51 per barrel, down about 2.4 percent for the week. West Texas Intermediate, the U.S. benchmark, lost six tenths of a percent to $59.24, off about 1.3 percent from the start of the week.

Markets have been hanging on words from ministers of the Organization of Petroleum Exporting Countries, who are meeting in Vienna this week to review market trends since crude oil prices started to collapse in June 2014. OPEC in November opted to keep production static despite the weak market and most observers expect the 12-member production group to toe the line when policies are announced later this week.

Crude oil prices are weakened by a market favoring the supply side. In a status report, the U.S. Energy Information Administration said total U.S. crude oil production for the week ending May 29 was 9.6 million barrels per day, a 14 percent increase year-on-year.

A report from the Organization for Economic Cooperation and Development said the global economy was gaining momentum, but the general sentiment was poor.

"The failure to trigger strong, sustainable growth has had very real costs in terms of lost jobs, stagnant living standards in advanced economies, less vigorous development in some emerging economies, and rising inequality nearly everywhere," OECD Secretary-General Angel Gurria said in a statement.

In an emailed report, analysis from Wood Mackenzie said Brent crude oil should stay at around $60 per barrel on average for the year and rise to $70 per barrel in 2016.