While they may be cheap to hire, they're not cheap to run, according to a report by government auditors at the Inspection Générale of Paris that Le Parisien newspaper has seen.
Despite the Velib scheme originally not being supposed to cost a penny to the public, the auditors found that in 2013, the total bill to run the system came to €16 million.
Paris City Hall has since confirmed that it forks out around €15 million a year, according to reports in the French media.
That total is apparently made up of €1.5 million in vandalism repair, €9 million in deployment to the outer suburbs, and maintenance costing between €3 million and €4 million.
The Paris Town Hall has yet to respond to The Local's response for more details on the breakdown of the costs.
The contract to run the bikes was signed by JCDecaux back in 2007, with the Paris mayor at the time Bertrand Delanoë suggesting that the bike scheme wouldn't cost a penny for the tax payer. In fact, he said it would bring in €3 million in revenue for Paris annually.
However, the contact no longer works in the city's favour, the auditors noted, accusing JCDecaux of a lack of transparency when it came to reporting their finances.
JCDecaux, however, has recently been granted an extra ten months on their contract to continue running the scheme for Paris until 2017, after which it is up for offer.
Jean-Michel Geffroy, head of JCDecaux subsidiary Somupi, said in a statement he "was sorry to hear of accusations that have been made in an effort to tarnish the proud reputation of Paris, JCDecaux, and Somupi".
He questioned why such a information had been published, not least when the contract for the future operator of the scheme was being put to tender.
The next operator will be announced in spring next year.
JCDecaux, meanwhile, has been chosen to develop similar bike systems in another 11 cities.
Since its 2007 rollout in Paris, the Velib scheme has become a major component in Paris's public transport system.
On average, 75 Velib bicycles are rented out each minute, or more than one every second.
Each bike is taken out an average of six times a day, and there have been over 292 million rentals since the launch nine years ago.
In August this year the scheme celebrated passing 300,000 subscribers.
While the bikes are hugely popular, the scheme has struggled with a massive theft and vandalism problem (see link below).