Crude oil prices started Thursday trading in the red, ignoring emerging positive sentiment from the Greek and Chinese economies.

Brent crude oil prices reversed course from overnight gains to open the day down about half a percent to $49.41 per barrel. West Texas Intermediate, the U.S. benchmark for crude oil prices, moved in parallel, trading at a 2015 low of $42.92 per barrel.

A string of reports this week indicated there may be an increase in demand for energy products in the latter half of 2015, though supplies continue to grow even as companies pull back on spending in the era of lower crude oil prices.

The U.S. Energy Information Administration this week cut its forecast for crude oil prices for 2015 and 2016. The agency expects Brent will average $54 per barrel this year and $59 per barrel in 2015, a decline of $6 and $8 per barrel from a July report, respectively. WTI should average about $5 less than Brent.

Thursday's declines follow the calming of a policy from Beijing to devalue its currency in an effort to arrest significant market declines. The People's Bank of China said Thursday the value of the yuan was back at market levels and there are no grounds for persistent depreciation.

Crude oil prices are off substantially from July levels after a series of crashes on the Chinese stock market and debt concerns emanating from Greece.

The Greek government said Tuesday it reached a bailout deal with lenders that would secure new much-needed finances in exchange for ambitious economic reforms, which lawmakers will review next week.

A report Thursday from the Greek Statistical Authority, known also as ELSTAT, said seasonally adjusted gross domestic product for the second quarter increased 0.8 percent in a surprise return to growth. Last year, however, second quarter GDP increased 1.5 percent.