Green made a name for himself quickly after being elected to Council in 2007, suing the city to prevent 11 libraries from closing because of budget woes and proposing to kill the much-hated DROP program.
Green, who co-sponsored a recently passed and praised business-tax-reform bill, said last month: "When I run for mayor, I'll resign."
* Councilman at-large
Jim Kenney is mulling a mayoral run in 2015 if he doesn't snag the Council presidency, a post he is said to be in the running for now as a dark-horse candidate.
Kenney, who has long focused on quality-of-life issues, recently saw Council pass a bill he introduced that will exempt new businesses from paying business taxes for two years if they hire local residents. He's now pushing a bill that would prevent restaurants from taking a portion of wait-staff tips to pay credit fees.
"I'm certainly looking at it. I haven't announced anything like at least one candidate that I know," Kenney said of running. "I just want to get through this election first, and then we'll see how it plays out."
* State Sen. Anthony
Hardy Williams briefly considered running against Mayor Nutter in the Democratic primary earlier this year.
He made an unsuccessful attempt at snagging the Democratic nomination for governor in 2010, but has said he's open to either running for governor again in 2014, or for mayor in 2015. Williams is the son of the late Hardy Williams, the former state senator who was the city's first African-American mayoral candidate.
* District Attorney
Seth Williams, has said publicly that people around the city have asked him to run for mayor. He faces re-election in 2013, but has not ruled out the idea of following the path of Ed Rendell, another district attorney-turned-mayor.
* City Controller Alan Butkovitz, who with his office's audits has been a frequent critic of Mayor Nutter's initiatives such as the 3-1-1 system, a tax on sugary drinks, and solar-powered street trashcans, along with troubled local agencies like the school district and Sheriff's Office.
Butkovitz easily won re-election to a second term in 2009 and plans to seek a third term in 2013 before deciding whether to seek the mayor's office.
"We're looking at it very closely," Butkovitz said. "There's a lot of people who want me to do it."
- Staff writer Chris Brennan
contributed to this report.