Submitting bids to the International Olympic Committee by Friday`s deadline were Rome; Madrid; Tokyo; Istanbul; Doha, Qatar; and Baku, Azerbaijan.
There were no surprises, as all six cities had previously announced their candidacies.
All six contenders have made previous bids, and two — Rome and Tokyo— have hosted the Olympics before.
Madrid is bidding for a third consecutive time, while Tokyo, Doha and Baku are making their second successive attempts. It is Istanbul`s fifth overall bid.
Doha is proposing to hold the games in September and October, outside the traditional July-August dates, to avoid the blistering summer temperatures in the Gulf country.
National Olympic committees had until Friday to notify the IOC of the names of any applicant cities.
The IOC will select the host city by secret ballot on Sept. 7, 2013, in Buenos Aires.
The six candidates must first submit detailed application files and letters of guarantee to the IOC by Feb. 15. The IOC executive board will meet in May to decide whether to cut any of the cities and approve a list of finalists.
Final bid dossiers will be submitted in January 2013, followed by visits to the cities by an IOC evaluation commission from February to April.
The IOC panel will issue a report assessing the technical merits of the bids at least one month before the vote. The cities will also make technical presentations to the IOC ahead of the meeting in Buenos Aires.
Rome, which hosted the 1960 Olympics, was the first of the cities to announce its bid months ago. The Italian capital lost to Athens in the race for the 2004 Olympics and hopes to stage the games on the 60th anniversary of the `60 Games.
Madrid, which has never held the Olympics, mounted unsuccessful attempts for the 2012 and 2016 Games.
Tokyo, host of the 1964 Games, finished third in the vote for the 2016 Games, which went to Rio de Janeiro.
Tokyo wants the 2020 bid to be a symbol of Japan`s recovery from the March 11 earthquake and tsunami that left almost 23,000 people dead or missing.
"I would like to thank members of the IOC for encouraging us to move forward for the reconstruction from the earthquake and tsunami damage earlier this year," Japanese Olympic Committee chief Tsunekazu Takeda said in a statement.
"We also appreciate the IOC members giving us valuable input and feedback on the previous bid for the 2016 Games. Learning from the experiences, I am committed to delivering the best possible games plan with improvements on every aspect."
Istanbul is back again after failed bids for the Olympics of 2000, 2004, 2008 and 2012.
Doha and Baku both failed to make the short list of finalists in the 2016 bidding.
The IOC executive board last week agreed to the Qatari city`s request for a Sept. 20-Oct. 20 time frame to avoid the summer heat, when temperatures can exceed 104 degrees.
Qatar has already won the right to host the first World Cup in the Middle East in 2022. The event will be held in June, and the desert country has proposed air-conditioned stadiums to beat the heat.
Qatar Olympic Committee general secretary Sheik Saoud Bin Abdulrahman called the IOC`s decision to accept the Doha bid "wonderful news for the people of Qatar and the entire Middle East."
"To have the opportunity to host the first ever Games in the Middle East will have a profound impact not just on sports development throughout the region, but also in encouraging a greater bridge between the Middle East and the wider international community," he said in a statement Friday.
Still considered a longshot is the bid from Baku, capital of oil-rich Azerbaijan. The Azerbaijan committee said a stadium was already being built for the Olympics on the outskirts of Baku and will be completed by next year.
The United States, South Africa and Dubai also considered bidding for 2020, but decided not to enter the race.