In my previous post I’ve talked about city and where to build them and how to increase you resources outputs with an oasis.

A nice spot should always have at least one oasis you need, from the eight type of oasis the hybrid ones are probably the best you can grab.
By hybrid I mean the one that gives food and another resource (iron, wood, stone) or a 50% grain bonus. Like this:
oasis

Requirement successfully to take an oasis :
First be sure to have a career center that gives you the right to have an oasis here the rule took from the previous post :

Career center in a city  with a Mansion

Level 10 career center = 1 oasis
level 15 career center = 2 oases
level 20 career center = 3 oases

Career center in a city  with a annexe

Level 10 career center= 1 oasis
level 20 career center= 2 oases

An oasis can only be attack with the plunder mode and once you destroyed all the troop in the oasis the oasis is your. If you don’t fulfill the first requirement the oasis will be left empty but will not belong to you, the army wills recover randomly every day.
Note: it seems to be an increase of 5-10 of every type of troops everyday but that was just an observation.

Tips

-The oasis can only be attacked in your 7×7 area of your city so you might want another city near it and have that oasis in it 7×7 to be able to help you strike that oasis.
-Since the building the career center to level cost a lump sum of resources why not build it to level 15, build a level one mansion and then grab an oasis.
you can destroy the mansion once you got you two oasis and you don’t have to level up your career center to level 20.

Note : It seems that the number of troop an oasis can have top at 200 of each except for the yellow turban and the swordsman that seems to top at 50 of each.

The strength of the unit in the oasis and how to grab an oasis from another player can be found here.

Update :

I added a thread about how to grab a oasis from another player here.