CHOOSE YOUR VARIETIES
First, please consider these questions:
1)  Do you want to grow olive trees for their fruiting capability (with potential for table use or oil)?
If so, you need at least two trees of two different varieties to ensure pollination. For example, one Leccino and one Maurino. For best results, buy more than two trees.

2)  Do you want to grow one olive tree only, but want it to bear olives?
Then you buy a Frantoio or a Taggiasca (aka Cailletier). Both are self-fertile and won’t need a partner to produce fruit (but you will get more olives setting fruit if you have another pollinator).

3)  Do you want to grow olive trees because they are beautiful, but you don’t want the fruit?
Then choose any number of any one self-sterile variety  (i.e. any variety other than the self-pollinating Cailletier, Frantoio or Taggiasca).

4) If you want to keep your tree(s) in pots you should read my recommendations for doing so here:

Olive trees in pots

 THEN . . .

DECIDE HOW MANY TREES YOU WANT
Space and access to the right microclimate will dictate how many olive trees you can grow in an area. See Planting Instructions for details.