About 50 percent of Pittsburgh and Mount Oliver property owners will see their tax bills drop under new assessments, with some of the city's southern, western and northern neighborhoods seeing the highest concentration of tax breaks and some eastern neighborhoods faring the worst, a study released Saturday said.

Overall, about 62 percent of property owners in the two municipalities will see lower tax bills or tax increases of less than 10 percent, according to the analysis by RealSTATs, a South Side firm that studies the regional real estate market.

The firm studied the impact of new assessments on 128,921 taxable parcels owned by individuals and companies in the city and Mount Oliver. Pittsburgh and the borough were the first municipalities in Allegheny County to see new assessments, which were ordered by Common Pleas Senior Judge R. Stanton Wettick Jr.

Some residents panicked when higher numbers began arriving in their mailboxes last month. On Jan. 12, Judge Wettick agreed to delay use of the new numbers until 2013.

However, city and Mount Oliver property owners still must move quickly to meet an April 2 deadline for filing formal appeals. Mayor Luke Ravenstahl on Friday proposed splitting the cost of appraisals with homeowners who need ammunition for appeal hearings, and Councilman Bill Peduto said he and others are working on a separate package of assessment aid.

About 69,000 property owners in the city and Mount Oliver will see their tax bills go down, and about 59,000 will see them go up, according to RealSTATs' projections. At least 23,000 will see them drop by $500 or more, and about 23,000 will see them rise by $500 or more, the firm said.

"Those 46,000 individuals, families, partnerships and corporations are the real winners and losers," RealSTATs said.

The study predicted that the greatest concentration of lower tax bills will be in the southern neighborhoods of Banksville, Beechview, Brookline, Carrick and Mount Washington; the northern neighborhoods of Brighton Heights and Marshall-Shadeland; and the western neighborhoods of Crafton Heights, Elliott, Sheraden and Westwood.