The state's Legislative Redistricting Commission, controlled by Republicans, had drawn new boundaries that eliminated O'Brien's district and created a new one, based in York County, with O'Brien's number, the 169th.
But the state Supreme Court threw out the proposed new map in a 4-3 decision last month. Until the redistricting panel crafts a new map that satisfies the courts, the boundaries adopted in 2001 remain in effect.
State legislative candidates had to file nominating petitions with voter signatures - at least 300 valid names for House candidates, 500 for would-be senators - by 5 p.m. Thursday as a first step toward securing spots on the primary ballot.
Three Philadelphians filed for O'Brien's seat, including his former chief aide, David Kralle; another Republican, John McCann; and Democrat Edward Neilson, a former official in the administration of then-Gov. Ed Rendell.
The three York County candidates, all Republicans, are expected to drop out unless state GOP leaders come up with a viable plan to change the boundaries and postpone the primary.
Six candidates filed Thursday for the South/Southwest Philadelphia House seat vacated by another new city councilman, Kenyatta Johnson. All Democrats, they include Jordan Harris, an aide to State Sen. Anthony Hardy Williams; former State Rep. Harold James; and Timothy Hanna, Damon Roberts, Edward Nesmith, and Fawwaz Beyha.
Five Democrats lined up for the North Philadelphia House seat vacated by new Sheriff Jewell Williams - including his daughter Jewel, Kenneth Walker, Gary Williams, James Johnson, Jose Miranda, and former State Sen. T. Milton Street Sr., who served prison time for failure to file tax returns.
Democrats Michael Ellis, Stephen Kinsey, and Karl Gamble are seeking the Germantown seat held by retiring State Rep. John Myers.
Petition challenges, based on invalid signatures or other irregularities, may knock many candidates off the ballot. But for now, about half the city's incumbent legislators face primary fights.
U.S. Rep. Bob Brady, chairman of the city's Democratic Party, has a primary challenger in former Municipal Judge Jimmie Moore. Former mayoral candidate John Featherman filed as the Republican candidate.
Another veteran Democrat, U.S. Rep. Chaka Fattah, drew only a Republican opponent, Robert Mansfield.
State Sen. Larry Farnese faces a Democratic primary challenge from John Morley. Alfonso Gambone filed for the GOP nomination.
Democrat James Clay submitted petitions to run against State Rep. Tony Payton; Jonathan Ramos, against State Rep. Angel Cruz.
In Northeast Philadelphia, Democrat Daniel Collins is challenging Rep. Kevin Boyle for the seat formerly held by Republican John M. Perzel, who pleaded guilty to charges involving use of state funds for politicking.
Democrat Norma McNeil is challenging State Rep. Maria Donatucci, who replaced her late husband, Robert Donatucci, last year.
In Center City, longtime State Rep. Babette Josephs faces a primary challenge from Brian Sims, a lawyer who was her campaign treasurer just two years ago.
In West Philadelphia, Democratic State Rep. James Roebuck has challengers in Darryl Kegler and Farimah Muhammad. Lemuel Thornton, Audrey Blackwell Watson, and Wanda Logan filed against state Rep. Vanessa Brown.
Will Mega Ashantee is opposing State Rep. Louise Williams Bishop in Overbrook/Wynnefield, and in Roxborough, Raymond Bailey filed against State Rep. Pamela DeLissio.
State Rep. Michelle Brownlee drew Democratic primary challenges from Andrew Kleeman, Michael Jones, and Takkeem Morgan.
In Northwest Philadelphia, State Rep. Rosita Youngblood is opposed by two other Democrats, Malik Boyd and Charisma Presley. Incumbent State Rep. Cherelle L. Parker, also a Democrat, is opposed by Bobbie Currie.
Two Democrats, Lamont Thomas and Sabriya Bilal, filed to run in the primary against former House Appropriations Chairman Dwight Evans.
And State Rep. Mark Cohen, who is seeking to extend his legislative career to 40 years, was challenged by Democrat Numa St. Louis.
Contact staff writer Bob Warner at 215-854-5885 or firstname.lastname@example.org.
Inquirer staff writers Angela Coulombis and Amy Worden contributed to this article.
Candidates for state and federal races in Philadelphia
This list of candidates in state and federal races in Philadelphia is based on Pennsylvania Department of State releases as of Thursday night, but additional candidacies are possible.
Incumbent: Vacated by Denny O'Brien (Republican). Challengers: David Kralle (R., Phila.), Leroy Wentz (R., York), Allan Case (R., York), John McCann (R., Phila.), Marc Woerner (R., York), Edward Neilson (D., Philla.)
Incumbent: Brendan Boyle (D). Challenger: George Weiss (R).
Incumbent: Kevin Boyle (D). Challengers: Al Taubenberger (R), Daniel Collins (D).
Incumbent: Michael McGeehan (D).
Incumbent: John Sabatina (D).
Incumbent: Michael O'Brien (D).
Incumbent: John Taylor (R). Challenger: William Dunbar (D).
Incumbent: Tony J. Payton Jr. (D). Challenger: James Clay (D).
Incumbent: Angel Cruz (D). Challenger: Jonathan Ramos (D)
Incumbent: W. Curtis Thomas (D).
Incumbent: Babette Josephs (D). Challenger: David Sims (D).
Incumbent: William Keller (D).
Incumbent: Maria Donatucci (D). Challenger: Norma McNeill (D)
Incumbent: Vacated by Kenyatta Johnson (D). Challengers: Damon Roberts (D); Harold James (D); Timothy Hannah (D), Jordan Harris (D); Edward Nesmith (D); Fawwaz Beyha (D).
Incumbent: James Roebuck (D). Challenger: Darryl Kegler (D), Farimah Muhammad (D).
Incumbent: Vanessa Lowery Brown (D). Challengers: Lemuel Thornton (D), Audrey Blackwell-Watson (D), Wanda Logan (D).
Incumbent: Ronald Waters (D). Challenger: Casey Ford (R).
Incumbent: Louise Bishop (D). Challenger: Will Mega Ashantee (D) .
Incumbent: Pamela Delissio (D). Challengers: Raymond Bailey (D), Linda Bateman, (R).
Incumbent: Michelle F. Brownlee (D). Challengers: Michael Jones (D); Takkeem Morgan (D), Andrew Kleeman (D).
Incumbent: Vacated by Jewel Williams (D). Challengers: James Johnson (D), Jose Miranda (D), Milton Street (D), Kenneth Walker (D), Jewel Williams (D., daughter of Jewell), Steve Crum (R), Gary Williams (D).
Incumbent: Rosita Youngblood(D). Challengers: Malik Boyd (D), Charisma Presley, (D)
Incumbent: Cherelle Parker (D). Challenger: Bobbie Parker (D).
Incumbent: John Myers (D), retiring. Challengers: Michael Ellis (D), Stephen Kinsey (D), Karl Gamble (D).
Incumbent: Mark Cohen (D). Challenger: Numa St. Louis (D).
Incumbent: Dwight Evans (D). Challengers: Sabriya Bilal (D), Lamont Thomas (D).
Incumbent: Lawrence Farnese (D). Challengers: Alfonso Gambone (R), John Morley (D).
Incumbent: Shirley Kitchen (D).
Incumbent: Mike Stack (D). Challenger: Michael Tomlinson (R).
Incumbent: Vincent Hughes (D).
Incumbent: Robert Brady (D). Challengers: John Featherman (R), Jimmie Moore (D).
Incumbent: Chaka Fattah (D). Challenger: Robert Mansfield (R).
Incumbent: Allyson Schwartz (D). Challengers: Nathan Kleinman (D), Joseph Rooney (R).