Of the 400,000 homeowners in Philadelphia, only 3 percent receive property-tax bills based on the true value of their real estate.

For the remaining 387,000, the amounts they are charged are wrong, and often wildly so - derived from assessments that, on average, are 39 percent off the mark, according to an analysis by The Inquirer.

The appraisals border on the randomness of Ping-Pong balls popped from a lottery machine, with winners and losers.

The neighborhoods where assessments are too high, and residents pay too much, include some of the poorest in the city. The most egregiously overassessed houses typically have market values under $69,000; their owners are overbilled $116, on average. The inflated appraisals, however, are not limited to distressed blocks. Nearly the entire Northeast, Mount Airy and Olney are overassessed.

Neighborhoods in the southern half of the city - with the notable exception of Southwest Philadelphia - are generally underassessed and homeowners undercharged. On the price scale, the properties with the most flagrantly lowball assessments tend to be above $200,000; those taxpayers get an average break of about $500 a year.

When Pennsylvania rated the accuracy of assessments in its 67 counties two years ago, the four adjacent to Philadelphia were in the top third. Chester County was No. 3 and Montgomery County No. 6, even though they had not conducted mass reappraisals since 1998.

Philadelphia came in 47th - startlingly low considering that, at least in theory, it reassesses annually and should have the most up-to-date values.

Last summer, in an exceptional push, 80 percent of all properties in the city were reappraised. The stated intent was to fix the increasingly glaring errors that were drawing fire from homeowners all over the city, who have complained that they could make no sense of the numbers or judge whether their bills were fair.

The new assessments, however, are just about as fallacious as the previous figures.

"They are so out of whack, it's unbelievable," said Robert P. Strauss, a property-tax expert and professor of economics and public policy at Carnegie Mellon University in Pittsburgh.

At The Inquirer's request, Strauss and Kevin Gillen, a real estate expert at the Wharton School of the University of Pennsylvania, conducted separate analyses of Philadelphia appraisals. The results of both studies were similar to The Inquirer's.

In recent years, as properties have appreciated, "assessment accuracy has worsened dramatically," Gillen concluded.

Throughout Pennsylvania, as in dozens of states, real estate levies are provoking historic levels of taxpayer wrath. And the temperature is rising, boosted by rate hikes imposed by cash-starved school districts and municipalities even as home prices sag. Critics and defenders agree that property taxes in Pennsylvania are increasingly chaotic and inequitable.

Philadelphia's system is all that, and worse. Article 8 of the Pennsylvania Constitution requires all assessments to be "uniform" – that all properties be taxed consistently at the same percentage of market value. The Inquirer analysis shows that is not the case in Philadelphia.

The property tax put $940 million into Philadelphia's coffers last year. Of that sum, $547.6 million went to the school district.

It is the job of the Board of Revision of Taxes - a seven-member panel appointed by county judges and independent of city government - to make sure every property owner is charged a fair share of the annual ante by accurately evaluating real estate.

That hasn't been happening.

This month, The Inquirer gave the board a summary of findings from the newspaper's analysis of publicly available BRT data. Administrator Barry Mescolotto, speaking for the board, said last week that he had not yet dissected the results but that, in general, such studies included too many atypical sales - for example, parent to child for $1 and sheriff's sales - that skewed the calculations.

Mescolotto said, however, that the board was well aware that its assessments lacked uniformity in many cases.

"There are uniformity problems," he said. "We're doing our best."