As of August 2017 Same-sex marriage is legally allowed (nationwide or in some parts) in the following countries: 

Argentina, Belgium, Canada, Colombia, Denmark, Iceland, Ireland, Luxembourg, Mexico, the Netherlands, New Zealand, Norway, Portugal, South Africa, Spain, Sweden, the United Kingdom, United States, and Uruguay. 

However, as of 2016 South Africa is the only African country where same-sex marriage is recognized, and no country in Asia allows same-sex marriage ceremonies, although Israel accepts same-sex marriages performed overseas.

Data source: Pew Research Center, August 2017