Store-bought oils are fine, as "true" voodoo / hoodoo shops gain their inventory, from priests and priestesses.
You can make your own, for that extra kick.
Since I specialize in jar spells, I use my oil to "dress" the following :
1. Taking a photo of my target(s), I dab their forehead.
2. After writing my petition, and folding it twice towards me, I dab its four corners.
3. A few drops on the candle, for the purpose.
You should say a prayer over each object, while "dressing" them, and in creation of its purpose.
~ Never Lost