Petalioi is an island complex in south-east of Euboea, in the homonymous gulf. It consists of 10 small islands and islets almost all uninhabited. The total area of the complex is 22.5 square kilometers. They belong to Karystos municipality, in Marmari municipal unit. The islands of the complex are: Megalonisos, Chersonisi, Avgo, Lamperousa, Louloudi, Makronisi, Pontikoniso, Praso, Tragos and Founti. The largest of them is Megalonisos. It has an area of 17 Km² and is uninhabited. The most of them are private islands and belong to Greek shipowners.