The Marlins will be sending significant money along with Marte to Oakland, the sources said.
Marte is hitting .306 with seven home runs and 25 RBIs for the Marlins this season. He missed time earlier this season with a fractured rib.
Marte, who is a career .288 hitter, is scheduled to become a free agent after this season.
Reporter Craig Mish first reported that a trade was close.