A monthly travelcard costs £135 ($174), according to a Deutsche Bank report - £33 ($43) more than Dublin, which was ranked second priciest city.
Auckland, where a ticket costs £95 ($123), came third, while New York City, at £91 ($118), came fourth, and Tokyo fifth at £86 ($111).
Transport for London (TfL) said the findings did "not show the true cost of transport in other countries".
The survey also found the cost of travel in the capital dropped since 2014, when commuters paid £165 ($213).
Source: Deutsche Bank
Its authors ranked London tenth most expensive for petrol, and the third for car hire.
Hong Kong had the priciest petrol, while Amsterdam was the most expensive for a daily car rental, the report said.
London's taxis fared slightly better, ranked 20th in a list of 47 cities, with Zurich topping the list for the most expensive fares.
For quality of life, London was ranked 33rd in the world, similar to other "mega cities" such as Tokyo, Paris and New York.
According to the report, these cities "rank very low" for quality of life, mostly due to "high living costs, crime, pollution and commuting time".
"This is highly subjective and one person's long commute may be another person's chance to catch up on Netflix," the report said.
"Megacity dwellers may also forsake short-term quality of life for aspirational reasons," the report added.
Wellington, in New Zealand, was ranked as the best city to live in in terms of quality of life, followed by Edinburgh, Vienna. Melbourne and Zurich.
In February, TfL revealed its fares income was down £90m last year.
TfL is currently planning to cut £16bn from its budget by 2020/21 as it  aims to become self sufficient with its operating costs.
The Mayor of London, Sadiq Khan, has frozen fares on buses and trams until 2020, but travelcard prices are set by train operating companies and so are not under full TfL control.
A TfL spokesman said: "London also has one of the most extensive set of travel concessions in the world with free or discounted travel for children, the over-60s, students and veterans."

John Clancy, Labour councillor for Quinton, beat closest rival Penny Holbrook in Monday night's ballot.
Ahead of the vote, he said providing new homes and improving existing social housing should be the authority's "top priority".
He will officially replace Sir Albert Bore on 1 December.
Mr Clancy, who has bid to become leader of the city council several times, was chosen in the ballot by the authority's 78 Labour councillors.
Updates on this story and others on Birmingham and Black Country
Sir Albert announced he would stand down as head of the self-styled "largest local authority in Europe".
A close call for a man waiting in the wings for more than a decade.
John Clancy has become leader of the Labour group after five attempts - and by just one vote. He will officially become leader of Birmingham City Council on 1st December when it's ratified at full council.
An English teacher for many years, he's no stranger to working in the public sector but he also had a spell as a solicitor, as well as a business lecturer.
His big message at a hustings last week was the council under his leadership can provide smarter financial decisions, political openness and free school meals for all primary age children.
Some critics from within the party are already saying they're worried he won't have the clout or the vision to make the huge and rapid improvement needed to keep government commissioners at bay.
The former Labour group leader's departure followed two other senior party figures, who resigned after criticising the way city was being run.
Ian Ward, the deputy leader of the local authority and councillor Barry Henley also stood for the position.
Mr Clancy, a former teacher and lecturer, has also pledged to widen access to free school meals for primary school children and expand regeneration outside the city centre.
Birmingham City Council has found itself under scrutiny from a government-appointed independent panel.
The panel was appointed at Sir Bob Kerslake's recommendation to oversee changes at the council.
Sir Bob's study was commissioned after a series of reports focussed on the council during an inquiry into the so-called Trojan Horse letter.
Public transport in London is the world's most expensive, a report says.
[NEXT_CONCEPT]
Birmingham City Council has elected a new leader - with the winning contender clinching the position by a single vote.