Capital with O

• Oslo

  Capital of Norway—totally fits!

• Ottawa

  Capital of Canada—perfect match.

• Oklahoma City

  Capital of the U.S. state of Oklahoma.

• Olympia

  Capital of Washington State (USA).

• Ouagadougou

  Capital of Burkina Faso—great pick.

• Oranjestad

  Capital of Aruba in the Caribbean.

• Oaxaca

  Capital city of the state of Oaxaca, Mexico

The words in the list Capital with O come from players of the word game City, Country, River.