A report by the Keystone Research Center has revealed that the city and county may be missing tens of millions of dollars in tax revenue each year. The five largest nonprofits in Pittsburgh, known as "The Big Five," own over $4 billion worth of tax-exempt property in Allegheny County. If taxed, they would generate an additional $27-million per year, according to the report. The city would also generate an extra $37 million per year.