Tiki torches fall into two categories: oil and gas. Gas torches are hooked up to natural gas lines and can burn indefinitely. Oil torches are filled with a particular type of fuel.
Tiki torches usually contains a lid where the wick is held in place. Fuel is placed inside the lid and the wick soaks the oil, allowing for the flame to be maintained. The flame on a tiki torch will last in proportion to how much oil can be held in the container.
The most popular fluid used for fuel in tiki torches is citronella oil. Paraffin oil, known most commonly as kerosene, also is very commonly used.
Citronella oil is an essential oil in lemongrass. It is often used as fuel for tiki torches for its odor that many find pleasant. Citronella also has the benefit of being a natural insect repellent.
Paraffin oil also is commonly used as a fuel for tiki torches because it burns cleanly and has less of an odor than citronella oil. Paraffin oil can be combined with citronella to get its insect-repelling benefits.