Arizona Governor Janet Napolitano is tipped to be homeland security chief, Democratic sources said.
Penny Pritzker, who chaired the finance team for Mr Obama's presidential campaign, could be commerce secretary.
And Bill Clinton has reportedly agreed to vetting of his affairs ahead of his wife becoming secretary of state.
Mr Obama's transition team has confirmed a number of other key advisers and top administration posts, while sources have been discussing the unconfirmed appointments.
Hillary Clinton, Mr Obama's defeated rival for the Democratic presidential nomination, is reported to be considering the secretary of state job, sources have said.
According to Reuters, former President Clinton has offered to allow an ethics review of future business and charitable activities to eliminate any conflict of interest if his wife accepts the senior position.
"He is definitely helping. He is not an obstacle at all," a Democrat source said.
Ms Napolitano was an early supporter and campaigner for Mr Obama's presidential bid.
She would head the homeland security department, created after the terror attacks in the US on 11 September, 2001.
Ms Pritzker is a billionaire and part of the Chicago family which founded the Hyatt hotel chain.
In other moves, Senior Democrat Tom Daschle is expected to be formally named as Health and Human Services Secretary, overseeing proposed reforms to the US healthcare system.
And Eric Holder is reported to be Mr Obama's choice to serve as attorney-general.
Key posts that were announced by Mr Obama's transition team on Wednesday include David Axelrod as senior adviser to the president, and Lisa Brown as staff secretary.