By Max Deveson
BBC News, Philadelphia
A high proportion of the voters were women
Another Democratic primary, another split along racial and generational lines.
Senator Hillary Clinton won in Pennsylvania by appealing to her core supporters: white voters, blue collar voters, female voters and voters over the age of 60.
Barack Obama again did well with black voters and young people.
But the demographics of Pennsylvania favoured Mrs Clinton, allowing her to take the state with a winning margin of 10 percentage points.
There were some encouraging signs for Mr Obama however, if his performance in Pennsylvania is compared to his results in neighbouring Ohio.
In Ohio, Mrs Clinton won among white men; in Pennsylvania, according to the ABC News exit poll, Mr Obama won the highest percentage of white men.
This allowed him to win over more men overall than Mrs Clinton.
Mrs Clinton's success with women continues, however.
She won 57% of the female vote in Pennsylvania, to Mr Obama's 43%.
With women making up 59% of the state's electorate, this translated into a strong advantage for the New York senator.
Support for the candidates is split along race lines
She also won a large majority of the senior citizen vote, but this situation was reversed at the other end of the age spectrum: Mr Obama took 61% of voters aged 18-29, to Mrs Clinton's 39%.
Mr Obama retained his strong support in the black community.
He won 89% of African-American voters, with Mrs Clinton taking only 11%.
But black turnout - at 14% - was lower than in the record 1984 and 1988 Pennsylvania primaries, so Mr Obama's dominance did not do him as many favours as it might have done.
Mrs Clinton did well among the 30% of voters who were union members, and the 40% of voters with a gun in their household.
But her standing among these groups does not appear to have improved compared to neighbouring states, suggesting that Mr Obama comments about "bitter" working class voters "clinging" to guns and religion have not worsened his position.
Mr Obama's traditional dominance among more educated voters was not so much in evidence.
He has enjoyed a nine-point advantage with this group on average in previous primaries, but in Pennsylvania he won voters with a college degree by only 51% to 49%.
Voter turnout was high across the state
And in Pennsylvania, college graduates made up some 46% of the electorate - compared with 38% in Ohio.
One group that has consistently refused to back Mr Obama has been white Catholics.
The group heavily favoured Mrs Clinton, by 71% to 29%.
And in Pennsylvania, white Catholics made up 33% of the electorate - double the average of earlier primaries.
Mr Obama could have demonstrated in Pennsylvania that he was able to cut into Mrs Clinton's core support - and he failed to do so.