This year’s mayoral primary was the most expensive election in Philadelphia history, with a $37.7 million price tag

This year’s Democratic primary for mayor was the most expensive in Philadelphia history.

The Democratic candidates and the political action committees that supported them spent about $37.7 million, an Inquirer analysis found.

The eye-popping price tag for the May 16 primary, which former state and city lawmaker Cherelle Parker won, was driven by several factors, including candidate Allan Domb’s prodigious self-funding, money from unions and wealthy individuals that fueled outside spending groups known as “super PACs,” and the large number of viable candidates in the race.

But the cash race alone didn’t determine the outcome.

» READ MORE: Inside Cherelle Parker’s winning campaign for Philly’s Democratic mayoral primary

Having lots of money was a prerequisite for candidates to be competitive this year, a fact that was made clear when former City Council members Maria Quiñones Sánchez and Derek Green dropped out because they couldn’t compete financially.

Parker handily won the primary despite her campaign and Philadelphians for Our Future, the super PAC that backed her, spending a combined $4 million to boost her, the third most of all the candidates. Parker’s victory in the crowded race can be credited largely to support from Black and Latino voters, rather than her campaign coffers.

She is heavily favored to defeat Republican nominee David Oh, also a former Council member, in the November general election thanks to Philadelphia’s overwhelmingly Democratic electorate. She would then take office in January, becoming the city’s 100th mayor and the first woman to hold the job.

The Inquirer’s analysis is based on campaign finance reports that were filed 30 days after the primary and, along with previous reports, provide the first comprehensive view into the total amount of money that was poured into the historic election.

The $37.7 million total is likely a slight undercount of the amount spent on the race because it does not include some money spent by independent expenditure committees that were not focused solely on the mayor’s race, including those that also sought to influence other elections, such as those for Council.

Individual campaigns spent more to boost candidates than the super PACs backing them.

Super PACs are independent expenditure committees that can collect checks above the city’s contribution limits so long as they do not coordinate with the candidates they are seeking to benefit. This year, those limits were $6,200 for donations from individuals and $25,200 from organizations.

In Philadelphia, the 2015 race was the first open mayoral election after the U.S. Supreme Court opened the floodgates to outside spending groups in its 2010 Citizens United decision, and Mayor Jim Kenney defeated State Sen. Anthony Hardy Williams. It is remarkable that super PACs outspent the campaigns themselves in that election. Kenney was backed by a super PAC funded largely by the building trades and teachers unions, while Williams had a super PAC in his corner that was funded primarily by three Main Line billionaires who supported his school choice policies.

Super PACs again played a crucial role in this year’s election — especially for Parker, who benefited from about $2 million in outside spending from the building trades — but they did not top the campaigns in spending.

The campaigns raised a staggering $30 million and spent $29.9 million, while the five super PACs that played significant roles in the mayor’s race took in $8.2 million and spent $7.7 million.

(The amounts raised and spent are not exactly the same due to a variety of factors, including outstanding debts, money brought into the race that was raised during other elections, and money that campaigns or PACs left in the bank.)

Four contenders had super PACs in their corners: Parker, former City Controller Rebecca Rhynhart, former Councilmember Helen Gym, and grocer Jeff Brown.

There was only one super PAC that figured prominently in the race that did not align itself with one candidate. The Coalition for Safety and Equitable Growth, which received much of its money from one of the conservative mega-donors who backed Williams in 2015, directed all of its resources toward attacking Gym.

The only top contender who did not benefit from a super PAC was Domb, a real estate magnate and former Council member who did not need anybody else’s money to run for mayor. Domb, who finished fourth, lavished $11.7 million of his own fortune on the campaign.

It’s been clear for weeks, however, that for all that spending, Domb got a historically poor showing. He spent a whopping $482 for each vote he won, easily making his the most inefficient Philly mayoral campaign in at least 16 years.

Brown did better, but not by much. He raised and spent somewhat less, only to place fifth with a cost of about $300 per vote, the second-least cost-effective campaign since 2007.

On the other end of the spectrum, Parker’s campaign spent $30 per vote received, the lowest of any candidate this year.

One reason this year’s election was so expensive on a per-vote basis is that despite all the money that was poured into the race, the campaigns and PACs failed to persuade significantly more people to vote.