There are many different olive varieties or cultivars in Greece for example: Manaki, Koroneiki, Lianolia, Chondrolia (aka Throumbolia), Tsounati.
Kalamata olives from the Greek mainland are the best known table olives in the world, but they are rarely used for olive oil. If you see the name Kalamata on a bottle of olive oil it refers to the mountainous region of Kalamata on the western Peleponnese, not to the olive variety. The Koroneiki olive is the main source of Greek olive oil though other local varieties such as Manaki and Tsouniti do find their way into the bottle.
Mani, Laconia and Sparta are also important producing regions. The olives are grown in small groves and sold either to private mills or to local co-operatives who, in turn, sell the oil on in bulk to large packers. Some oil is sold locally from the mill. Very little Greek oil is bottled by the grower. The pattern is very similar in Crete, the other major producing region in Greece. Olives are also grown on the other islands but you will only see the oils from these olives on your holidays.
Greek olive oil is consistently herbaceous in character but varies from fresh and grassy to dry and hay-like depending on the growing conditions. Other varieties are grown in the north of the country and in the islands but most of this oil is consumed at home.