Perfume oils can be very convenient for travel because a small roll-on bottle takes up hardly any space.
Lily Essences bottles are 5 mL, making them easy to fit into a purse, cosmetic bag or travel bag.
For U.S. airport security, TSA's carry-on liquids rule generally permits liquids in containers of 3.4 ounces/100 mL or less, subject to the applicable 3-1-1 liquids requirements. A 5 mL bottle is well below that container-size limit.
Keep the cap closed and, when practical, carry the bottle upright.
The difficult part of traveling with a small perfume collection isn't fitting it in your bag.
It's choosing which one to bring.