Saudi Arabia and most of its neighbours will celebrate the Eid al-Fitr feast on Tuesday to mark the end of the holy fasting month of Ramadan.
Bahrain, Kuwait, the United Arab Emirates, Qatar and Yemen will also start the holiday on Tuesday.
The timing of Eid can vary in different countries depending on the sighting of the new moon, which marks the start of the month in Islam's lunar calendar.
Regional stock markets are closed during the holiday. The Saudi bourse, the Arab world's largest, has the longest break and will re-open on 6 October.