HFO may refer to:

• HealthForceOntario
• Heavy fuel oil
• Hybrid fibre-optic
• Hydrofluoroolefin
• Hydrous ferric oxides
• Hypofluorous acid
• Halbleiterwerk Frankfurt (Oder)

• List of populated places in North Sumatra
• List of populated places in Norway
• List of populated places in Poland
• List of populated places in Portugal
• List of populated places in Russia
• List of populated places in Sakarya Province
• List of populated places in Samsun Province
• List of populated places in San Marino
• List of populated places in Slovakia
• List of populated places in Slovenia
• List of populated places in South Ossetia
• List of populated places in Spain
• List of populated places in Svalbard
• List of populated places in Sweden
• List of populated places in Switzerland
• List of populated places in the Czech Republic
• List of populated places in the Faroe Islands
• List of populated places in the Nagorno-Karabakh Republic
• List of populated places in the Republic of Ireland
• List of populated places in the Republic of Macedonia
• List of populated places in the United Kingdom
• List of populated places in Ukraine
• List of populated places in Åland
• List of populated places in Çankırı Province
• List of populated places in Çorum Province