Some collectors just collect bottles with the word "oil" embossed on them. The quack docters from the 1800s sold many a medicine bottles as snake oil or majic oil with a promise of miracle cures.

The few oil bottles I have are from left to right:
Singer Sewing machine oil
Sewing machine oil with cork and oil in it
Rare 7 1/2" Lockport, NY Gargling oil
Cobalt newer Lockport, NY Gargling oil
a round Kickapoo Indian Oil
Standard Green 5" Lockport, NY Gargling oil