New Mexico Governor Bill Richardson, 60
As Governor and former energy secretary, he brings administrative experience. As former UN ambassador, he has the credentials to deflect criticism of Mr Obama as 'naive' in foreign policy. A Hispanic, he can deliver the Latino vote. But he is not a draw for blue-collar whites.
Former North Carolina governor John Edwards, 55
Has the working-class appeal that Mr Obama needs to get the blue-collar vote. His anti-Washington special interests image fits well with Mr Obama's. But may not be interested in being No. 2 again.
Senator Joe Biden, 65
As Senate Foreign Relations panel chief, he adds expertise to Mr Obama's resume. As a Washington insider, he contradicts Mr Obama's call for change. Lacks executive experience.
Virginia Senator Jim Webb, 62
Former president Ronald Reagan's navy secretary and Vietnam War veteran will add heft on national security matters. But, as a first-term senator, does not add experience.
Could complement Mr Obama's bipartisan agenda of reaching social/cultural conservative voters with her opposition to gay marriages and support for the right to own guns. As a woman, may not appeal to voters tentative about what is already a non-traditional ticket.
