According to Guinness World Record, where is the largest "self contained" oasis in the world?

The word oasis came into English via Latin: oasis from Ancient Greek: ὄασις óasis, which in turn is a direct borrowing from Demotic Egyptian. The word for oasis in the later attested Coptic language (the descendant of Demotic Egyptian) is wahe or ouahe which means a "dwelling place".

The largest self-contained oasis in the world is the Al-Ahsa Oasis. Located in south-eastern Saudi Arabia, there are more than 2.5 million palm trees in the oasis, which is fed from a huge underground aquifer, which allows agriculture all year round in a region that is otherwise sand desert. The oasis is named after the Al-Ahsa region in which it lies, and occupies around 85.4 square kilometres (32.9 square miles) irrigated by the flow of more than 280 artesian springs.