The registration activity has been furious - about twice what the city has seen in previous presidential primaries - said Bob Lee, administrator for the Board of Elections.
And much of the activity has been in Center City and University City, areas seen as favoring Obama.
"The largest increase in voters seems to be in wards that would most likely be Obama wards," said Dan Fee, a Democratic political consultant who supports Obama.
The Clinton campaign disagrees.
"We don't cede that ground," said campaign spokesman Brendan Gilfillan. "Our efforts will allow us to dispute that notion very strongly."
Gilfillan said that Clinton didn't pour as much money into voter-registration campaigns, but that the volunteer efforts were "very intense" nonetheless.
Nowhere was the activity more furious than the 27th Ward, which includes the University of Pennsylvania. The school's nonpartisan student organization, Penn Leads the Vote, held a registration fest five days before the March 24 deadline under the theme "Civic Virtue and Free Food." The results of that and other efforts: nearly 2,800 new Democrats, a 30 percent increase since November.
"That's a record increase over what was a record increase, so it's doubly remarkable," said Penn president Amy Gutmann.
Democratic ward leader Carol Jenkins said the 27th was split among students, educated white liberals, and African Americans - "the perfect Obama supporters," she said.
While Jenkins said she had not pushed either candidate, her committee did endorse Obama, and his campaign has been far more active in the area than Clinton camp, she said.
Also in the top 10 wards in the percentage of new Democrats were the 24th and 20th Wards, which encompass Drexel and Temple Universities, respectively, and the 46th Ward, a mixture of Penn and West Philadelphia.
