Some 554 suspects were arrested in 2015/16, compared with 406 during the previous 12 months, Transport for London (TfL) said.
A new campaign has been launched to encourage victims to come forward by demonstrating that each report helps to build a picture of offenders that can ultimately lead to their identification and arrest.
It features a film showing a businessman with a pixelated face giving a presentation in an office while the voices of women recalling unwanted sexual behaviour on public transport are heard.
As each woman recounts her experience, the man's face becomes increasingly visible, until he can be seen clearly and is then apprehended by police.
London Mayor Sadiq Khan said keeping passengers safe is his top priority.
“I want all women and girls to feel confident travelling on our transport network,” he said.
“This vital campaign highlights how any form of unwanted sexual behaviour is unacceptable and victims must be given the right support when they report offences.”
Since TfL and the police launched the Project Guardian partnership in 2013 with the aim of eliminating sex attacks from public transport, the number of annual reports has doubled, from 1,023 in 2012/13 to 2,087 in 2015/16.
Siwan Hayward, TfL's head of transport policing, said: “We are determined to eradicate unwanted sexual behaviour on the transport network. It is never okay.”
Superintendent Jenny Gilmer, of British Transport Police, urged victims to report incidents as soon as possible and reassured them that they will be taken seriously.
She said: “Time is of the essence so we can exploit all evidence-gathering opportunities.
”Every report with as much detail as possible helps to build a picture of the offender.“
The campaign film can be viewed on YouTube.
Sexual offences on public transport can be reported to the police by texting 61016 or calling 101.