Olive

Olives are a fruit grown from the Olive tree, and are the primary source of Olive oil. While neither the Olive tree nor Olives exist in-game, the reason for the otherwise inexplicable full stock of Olive oil throughout Geilinor has been brought to light thanks to Mod Mat K's response to a reddit thread   [1]. He wrote the following:

"Terragon the Lord of Asgarnia and protector of the Free People's of Geilinor sat under the midday sun basking in its heat. As he looked around him he saw the heat haze rise from the ground making it seem as if the horses in the fields gilded over the ground. That is when he saw it.

''In the distance a horse lay still on the grass next to a strange looking tree, a tree which Terragon had not seen before. He approached the horse and saw that it had died and around it's body was a strange green berry, almost olive in colour.''

''As he stood there staring at the dead horse a female voice cackled behind him, and the unmistakable sounds of the ultra fertile soil spell rocketed past his ears. The strange berries started to germinate before his eyes.''

"Who are you? What are you doing?", exclaimed Terragon.

"My name is Aggie and I am allergic to horses so I am going to kill them all using this poisonous berry!"

''Terragon immediately tried to collect every berry he could find and put them into a basket. "I will stop you by crushing all these berries which I have now decided to call Olives because of their colour. You will not kill all the horses in Gielinor!"''

''The battle raged for 16 years as Aggie spawned olive trees and Terragon crushed the olives until Aggie had a realisation. In the latest strain of olive Aggie added a poisoned gas which was released when it was crushed but not detectable by humanoids.''

''And thus it was that although Terragon destroyed all the olives, he inadvertently caused the death of all horses in Gielinor. However, he single-handedly made the entire stock of olive oil in Gielinor.''

True story." ~ Mod Mat K

It is currently unknown at what time during Gielinor's history this event occured, as Aggie could very welll be much older than her appearance lets on; however, the shelf life of Olive oil and the constant restocking of the product in NPC stores suggests that this event occured in Gielinor's recent history.