Of course, much will depend on the candidates, the overall political environment, and the ability to reach unaffiliated voters. Even in close districts, Republicans have done well in recent years, beating back Democratic challenges. And at the moment, most analysts see a strong 2014 for the GOP.
Still, the numbers give a sense of the playing field in the seven Philadelphia-area races with either open seats or closely balanced districts, now that both Pennsylvania and New Jersey have passed their filing deadlines.
Voter-registration stats are from March 21 in Pennsylvania and March 30 in New Jersey, as supplied by state election officials. Election results for 2012 are from the Cook Political Report, as is the Cook PVI - Partisan Voter Index - which measures how far each district leans Democratic or Republican in presidential races.
Pa. Sixth District
Parts of Chester, Montgomery, Berks, and Lebanon Counties.
Incumbent: Jim Gerlach (R) is retiring.
Registered Democrats: 183,294 (39 percent).
Registered Republicans: 203,317 (44 percent).
2012 presidential winner: Mitt Romney, 51-48.
Cook PVI: R+2.
Notes: Democrats had little hope here before Gerlach's retirement, but the open seat makes for a more competitive environment. Still, the district has been tilted to the right by redistricting, and Romney did better here than in any other district around Philadelphia.
Candidates: Chester County Commissioner Ryan Costello is the GOP pick to take on physician Manan Trivedi, a Democrat, who twice lost to Gerlach.
Pa. Seventh District
Parts of Chester, Delaware, and Montgomery Counties.
Incumbent: Patrick Meehan (R).
170,194 (36 percent).
240,154 (50 percent).
2012 Winner: Romney, 50-49.
Cook PVI: R+2.
Notes: By registration numbers, Meehan has the most heavily Republican district in the region. He's heavily favored.
Candidates: Meehan faces a Democratic challenge from La Salle University political science professor Mary Ellen Balchunis.
Pa. Eighth District
Parts of Bucks and Montgomery Counties.
Incumbent: Mike Fitzpatrick (R).
Registered Democrats: 203,343 (42 percent).
Registered Republicans: 199,761 (42 percent).
2012 Winner: Romney, 49-49 (won by decimal points).
Cook PVI: R+1.
Notes: It's the region's most closely divided district. Democrats have a slight numerical edge. But Fitzpatrick has been resilient - how else to explain his impressive 13-point victory in 2012, well ahead of Romney?
Candidates: Fitzpatrick says this will be his last run for Congress. Democrats have a May 20 primary between Army veteran Kevin Strouse and businesswoman Shaughnessy Naughton.
Pa. 13th District
Parts of Montgomery County and Philadelphia.
Incumbent: Democrat Allyson Y. Schwartz is running for governor, leaving the House contest open.
Registered Democrats: 294,322 (60 percent).
Registered Republicans: 133,726 (27 percent).
2012 Winner: President Obama, 66-33.
Cook PVI: D+13.
Notes: In this heavily Democratic district, the biggest contest is expected to be the party's May 20 primary, which features four contenders.
Candidates: Physician Val Arkoosh, State Rep. Brendan Boyle, State Sen. Daylin Leach, and former U.S. Rep. Marjorie Margolies. Republicans have two candidates running: Dee Adcock, a businessman who ran against Schwartz in 2010, and Beverly Plosa-Bowser, a retired Air Force colonel.
N.J. First District
Parts of Camden, Burlington, and Gloucester Counties.
Incumbent: None. U.S. Rep. Robert E. Andrews, a Democrat, resigned in February.
Registered Democrats: 198,135 (40 percent).
Registered Republicans: 69,793 (14 percent).
2012 Winner: Obama, 66-34.
Cook PVI: D+13.
Notes: The open seat has drawn seven candidates, even though this is historically one of the least-competitive districts in the region. After the two House districts in Philadelphia, this is the most Democratic territory in the area (by voter counts).
Candidates: The most powerful Democrats in this district have uniformly lined up behind state Sen. Donald Norcross, brother of South Jersey power broker George E. Norcross III. (George Norcross is also majority owner of the company that publishes The Inquirer.) Donald Norcross faces a primary fight from Logan Township Mayor Frank Minor and Marine Frank Broomell Jr. The Camden County Republican organization has pinned its hopes on ex-Eagles linebacker Garry Cobb. He faces GOP competition from Lee Lucas, Claire Gustafson, and Gerard McManus.
N.J. Second District
Atlantic, Cape May, Cumberland, and Salem Counties and parts of Gloucester, Burlington, Camden, and Ocean Counties.
Incumbent: Frank LoBiondo (R).
Registered Democrats: 127,436 (27 percent).
117,841 (25 percent).
2012 Winner: Obama, 54-46.
Cook PVI: D+1.
Notes: This is one of just 17 districts in the country that elected a Republican to Congress, but went for Obama in 2012. Democrats have a slight edge in voters, but the race will likely be decided by the huge swath of nearly 223,000 unaffiliated voters.
Candidates: LoBiondo is being challenged in the GOP primary by Mike Assad, who also tried to unseat him in 2012. National Democrats are behind William Hughes Jr., whose father held the seat for 20 years before LoBiondo. Dave Cole, a former Obama administration aide, is running against Hughes.
N.J. Third District
Parts of Burlington and Ocean Counties.
Incumbent: Republican Jon Runyan is retiring.
Registered Democrats: 131,418 (27 percent).
Registered Republicans: 122,152 (25 percent).
2012 Winner: Obama, 52-48.
Cook PVI: R+1.
Notes: This is another of the 17 seats where Obama and a House Republican both won in 2012. Democrats see Runyan's exit as an opportunity. Still, the district has been in GOP hands for all but two years in recent memory, and redistricting in 2010 took out Democratic stronghold Cherry Hill.
Candidates: Tom MacArthur, former mayor of Randolph, is the pick of the GOP establishment and is campaigning as a moderate, but he faces a June 3 primary against conservative activist Steve Lonegan, who has a long history of stirring up grassroots support. National Democrats are behind Burlington County Freeholder Aimee Belgard, but she has primary competition from Howard Kleinhendler, who ran in a neighboring district in 2010.