U.S. Treasury yields gave up some losses Thursday amid a report that OPEC members could be ready to cooperate on a crude production cut.

Earlier in the day, yields plunged to levels not seen since 2012, in some cases, as worries over global growth and the effectiveness of central bank policy sparked huge demand for safe-haven assets. As stocks sold off Thursday morning, 30-year bond futures hit their highest level in 40 years, according to Bespoke Investment Group.