Cities with high collection rates, the study found, adhere to strict timetables about when and how to go after deadbeats. Philadelphia tax collectors, on the other hand, have greater leeway in using collection tools and apply them inconsistently.
The 70 percent of taxes deemed "most likely uncollectible" include properties in less desirable neighborhoods, homes in poor condition, owners with high tax debt and those who have been delinquent for a long time.
Those factors decrease the likelihood of a property owner responding to the city's collection efforts and help explain why Philly and other cities with high poverty have lower collection rates.
Still, Philly is leaving money on the table.
"The city certainly could do better," said Thomas Ginsburg, project manager at Pew's Philadelphia Research Initiative and author of the study.
The debate over property-tax delinquency took center stage earlier this year as the city moved toward adopting the Actual Value Initiative, or AVI, the overhaul of the property-assessment system Mayor Nutter has promoted. AVI, which aims for more accurate assessments of property values, begins next year and will result in higher taxes for many homeowners whose properties have been undervalued for years.
A recent PlanPhilly/ Inquirer investigation highlighted the city's poor performance on collections and revealed a ripple effect of problems for neighborhoods with high delinquency.
Nutter in February announced a series of measures intended to crack down on tax deadbeats, including the creation of a chief collections officer.
The administration says it will collect $28 million more in delinquencies next year, although that number includes more taxes than just the real estate levy.
On Twitter: @SeanWalshDN