Greek owners feature heavily on a list of tankers detained in Yemen by Houthi militias.
Saudi Arabia has said it fears the vessels will be destroyed as part of the civil war that is tearing the country apart.
A list provided to TradeWinds by the Embassy of Saudi Arabia shows 17 tankers, a gas carrier and a bulker carrying wheat have been held at the port of Hodeidah for more than 26 days in some cases.
The tankers are carrying more than 200,000 tonnes of oil, mainly diesel and petrol, in cargoes of up to 27,000 tonnes.
Greek owner Belavero Maritime's 36,000-dwt Bahia Damas (built 1991) arrived on 29 March with a cargo of diesel and petrol, Saudi Arabia said, while Evalend Shipping's 20,000-dwt Volante (built 2008) has been stuck at the port since 26 March with more than 16,000 tonnes of diesel.
Evalend has another vessel on the list.
Also at the port are tankers controlled by Greek owners, including Perosea Shipping's 13,100-dwt Liaki Freedom (built 2007), NGM Energy's 25,200-dwt Carpe Diem II (built 2010) and four out of five ships controlled by Eurotank Maritime, plus one from Oryx Shipping.
UAE ships held
UAE owners Folk Shipping, Emirates Shipping, OBN Ships Trading and Betatank M also have vessels detained, as does Safe Sea Services of Lebanon.
The lone LPG carrier is Spanish owner Global Gas' 7,000-cbm Celanova (built 2003).
The ships are being held at anchorage outside Hodeidah, which is under Houthi control, despite the port being free of any other ships, Saudi Arabia said.
The Yemen Comprehensive Humanitarian Operations (YCHO) centre in Saudi Arabia has contacted the United Nations to express its concern over the issue.
The Embassy said: "This move hinders relief efforts, prevents aid from properly reaching the Yemeni people, and grows the black market for goods while enabling the Houthi militias to benefit and extend the war further.
"There is a strong fear that the Iranian-backed Houthi militias intend to destroy these ships, which would create an environmental disaster in the Red Sea in addition to depriving the Yemeni people of intended aid."
The Saudi-led coalition is responsible for issuing approvals that allow vessels to dock and has granted permits for all the 19 ships.
