Gold surged more than 2 percent and was on track for its biggest one-day jump in seven weeks on Friday.
U.S. oil prices tumbled more than 1 percent, after weekly data showed U.S. drillers added rigs for only the second time this year.
U.S. stocks closed at session highs Thursday, with health care stocks leading, ahead of the highly anticipated employment report due Friday morning.
U.S. government debt prices were higher on Thursday morning as investors looked towards the release of data and eyed OPEC's meeting in Vienna.
U.S. stock index futures pointed to a higher open, amid gains in oil prices, as traders awaited Yellen's speech scheduled for midday.
U.S. stock index futures pointed to a lower open Friday after the May jobs report showed creation of 38,000 jobs, well below expectations.
European stocks ended mixed to slightly lower by Thursday's close, as investors digested the latest news out of OPEC and from the ECB.
The dollar fell to its lowest against the yen in more than two weeks.
Gold was little changed on Thursday as the dollar cut losses after the ECB said it made only marginal upward adjustments to its inflation projections.
WTI rose after data showing a weekly drawdown in crude stockpiles helped it recover from OPEC's decision.
Japan's Nikkei tumbled after the government moved to delay a sales-tax hike for more than two years, bucking mostly higher markets around the region.
U.S. stocks closed well off session lows Wednesday, helped by an intraday recovery in oil prices and better-than-expected manufacturing data.
U.S. sovereign bond prices were mixed Wednesday ahead of the release of the Federal Reserve's Beige Book.
European stocks finished in the red on Wednesday as sharp declines from European banks and miners weighed on sentiment, ahead of a number of key policy events.
The U.S. dollar hit its lowest level in two weeks against the yen after Japan delayed a sales tax hike for longer than expected.
Gold turned negative on Wednesday, as the dollar briefly pared losses following U.S. manufacturing data.
U.S. stock index futures pointed to a lower open on Wall Street Thursday morning as traders eyed data and OPEC's meeting in Vienna.
Oil prices closed off their session lows after OPEC sources said the group was likely to consider a new output ceiling.
Most major Asian markets ended lower Wednesday after mixed signals from China's PMI data and better-than-expected Australian economic growth.
U.S. stocks closed mixed Tuesday, the last trading day of May, as investors eyed economic reports for indications on the timing of the next rate hike.