Fifty-five will be awarded based on the statewide vote, which should be available Tuesday night. Another 103 delegates will be awarded based on the vote in individual congressional districts. All delegates will be awarded proportionally, as they are in every Democratic contest.
The distribution of delegates among congressional districts raises the possibility that one candidate could win the statewide vote and the other could win more delegates, but the statewide vote would have to be very close.
The delegates are weighted heavily toward urban and suburban areas because Pennsylvania, like other states, apportions congressional district delegates based on Democratic voting strength in the most recent presidential and gubernatorial elections.
Under the formula, the 2nd Congressional District, which includes part of Philadelphia, has nine delegates at stake, more than any other district. The 9th Congressional District in the south central part of the state has the fewest, with three delegates at stake.
I'm in the 2nd.
...here's a full district delegate breakdown for real geeks (.pdf).