The trip by London Mayor Ken Livingstone and officials to Cuba and Venezuela cost tax payers nearly £36,000, a breakdown of costs reveals.
Mr Livingstone said the expenses were "modest"
The mayor's personal visit to Venezuela to sign an oil deal was cancelled, and he returned from Cuba leaving his officials to go on to Venezuela.
A preliminary estimate of the total costs was made public after calls by members of the London Assembly.
Mr Livingstone said the cost of the trip was "modest".
The mayor and four officials stopped in Cuba, at a cost of about £20,000, including £16,991 in flight tickets.
When Mr Livingstone's plans to go to Venezuela fell through, four other officials who had travelled from London to Venezuela at a cost of nearly £16,000, including £12,948 on flights, returned home.
The mayor's office said it had yet to calculate the costs of unused tickets and other facilities used by the entourage.
Mr Livingstone's political opponents have told BBC London political editor Tim Donovan the tour raised questions about judgement and was "humiliating and embarrassing".
They are also asking how Londoners are going to benefit from the visit.
The mayor's office said Mr Livingstone was invited by Lord Moynihan - chair of the British Olympic Association - to attend a sports congress in Cuba.
After Cuba, the mayor was scheduled to fly to Venezuela to sign an oil deal with President Hugo Chavez, which will ensure subsidised Venezuelan oil for London.
The mayor said: "Since I was first elected in 2000, I have spent an average of just ten days a year - less than 3% of the time - on mayoral trips abroad.
"Given that Cuba plays a central role in the international Olympic and sporting movement, particularly in fields like boxing, the costs of my visit to Cuba are modest and in line with the costs incurred on other mayoral trips.
"Similarly, the costs of the advance trip by key staff to Venezuela to prepare for the visit were also modest."