The move came amid tension between the United States and Iran over its nuclear programme, and a warning this month by Iran's supreme leader that world energy flows could be endangered by any US "wrong move" against Tehran.
WAM said transport ministers of the six Gulf countries "adopted an emergency plan to be implemented on (Gulf Arab) seaports if Hormuz and Bab al-Mandab straits are closed".
The agency gave no details of the plan, agreed at a meeting in the UAE capital Abu Dhabi.
Iran's Supreme Leader Ayatollah Ali Khamenei's remarks were interpreted by some oil traders as a hint that the Islamic Republic could deliberately disrupt energy shipments, using its strategic position on the Strait of Hormuz, a crucial passageway for oil tankers.
Iran is under pressure to rein a nuclear programme which the US and its allies suspect is intended to eventually produce nuclear arms. Sanctions could be imposed on Tehran, and the United States and Israel have not ruled out military action.
Some of the oil heading westwards by tanker from the Gulf passes through Bab al-Mandab at the mouth of the Red Sea, which leads to the Suez Canal and the Suez-Mediterranean pipelines.