Fare evasion on London's buses has nearly doubled in the last four years, according to the Liberal Democrats.
Fare evasion is higher on bendy buses
A freedom of information request shows in 2003 the evasion rate was 2.2% of the total number of journeys compared to 3.9% in 2007.
The party says fare evasion on bendy buses cost £6.4m last year. The total cost it claims is £52.3m.
But Transport for London (TfL) disputed the figures saying the total cost of fare evasion was £35m.
The information obtained by the Lib Dems showed there were 1.8 billion bus journeys taken in London in 2006/7.
It said there were about 58 million fare evasions in that period, with 7.2m people dodging the fare on bendy buses.
The party has multiplied number of fare evasions by the standard bus fare of 90p.
But TfL said it should be multiplied by 53p as this is the average revenue it gets per passenger, per bus journey.
TfL said it gets more than £1bn-a-year from bus fares.
Brian Paddick, the Lib Dem London mayoral candidate, said: "Only the other day I overheard a Londoner describing a bendy bus to a tourist as the 'free bus'.
"No wonder nobody pays."
A statement from TfL said: "TfL has been working hard to combat fare evasion and over the last year the rate of fare evasion has gone down, and we have also prosecuted more fare dodgers than ever before."