Official data on U.S. crude oil inventories showed an increase, adding to supply-side concerns and sending oil prices lower for a second day Thursday.

A rally in crude oil prices faded Wednesday after industry data from the American Petroleum Institute showed domestic crude oil inventories grew by 9.9 million barrels for the week ending Feb. 26. Official government from the U.S. Energy Information Administration show stockpiles grew by 10.4 million barrels.

"At 518.0 million barrels, U.S. crude oil inventories are at historically high levels for this time of year," EIA said in a weekly report.

Brent crude oil prices moved lower before the start of trading in New York, losing 0.7 percent to $36.66 per barrel. West Texas Intermediate, the U.S. benchmark price for oil, moved down in parallel to hit $34.42 per barrel before the opening bell.

Oil prices are off about 40 percent from this time last year as high supplies balance against lackluster demand in a weakened global economy. Momentum in energy markets this year was influenced by the pace of growth in China, with two major stock market crashes reported since January.

Crude oil prices moved higher earlier this week after the People's Bank of China said Monday it was cutting its interest rates for banks by a half percent to influence lending. Oil moved lower during the next session after Moody's Investors Service said it had lingering questions about Chinese economic policies.

The annual session for Chinese political leaders kicked off Thursday in Beijing. Of the estimated 6,000 proposals submitted to a political advisory board, about one-third were related to economic issues.