European caution trumped the market reaction to a surge in the Japanese stock market, sending crude oil prices slightly lower at the opening bell Wednesday.

Brent crude oil prices moved down by a fraction of a percent to $49.30 per barrel at the start of trading Wednesday in New York. West Texas Intermediate, the U.S. benchmark, inched marginally below the close of the previous session to start the day at $45.72 per barrel.

Crude oil prices are pressured by indications of weak growth in European and Asian markets. European Central Bank President Mario Draghi said Thursday he was keeping key interest rates unchanged at near zero percent. While recognizing the slow recovery in the European economy, Draghi said he'd use "all the instruments available" to push momentum forward.

European Commission President Jean-Claude Juncker said the crisis is not over for a European economy that averted a fiscal emergency with the latest row over Greek debt issues.

"The crisis is not over," he said in a speech on the state of the European Union. "It has just been put on pause."

Though gross domestic product and employment figures are improving, progress has been slow and is at risk from economies outside the euro area.

Markets this week were damaged by ongoing concerns about the Chinese economy, highlighted by data this week showing exports were down. Japan's Nikkei gained more than 7 percent, however, for its strongest day since 2008.

Japan, the world's third-largest economy, announced in February it exited two quarters of consecutive recession. Last month, the government reported the economy declined at an annualized rate of 1.6 percent from April to June.

Nikkei's rally lifted futures on Wall Street, suggesting the early declines in crude oil prices might not last the session.