The best oil to use in a Zippo lighter is Zippo's own lighter fluid, which is specifically formulated for the lighter's design. This fluid is designed to provide a consistent flame and is safe for use in Zippo lighters. The use of Zippo's lighter fluid ensures optimal performance and longevity of the lighter.

Zippo's lighter fluid is a high-quality, paraffin-based fuel that is designed to ignite easily and burn cleanly. It is formulated to be safe for the lighter's internal components and to provide a reliable flame. The use of non-Zippo fluids can lead to a variety of issues, including poor flame performance, damage to the lighter, and potential safety hazards. According to Zippo's official guidelines, their lighter fluid is the only recommended fuel for their lighters. This is because it is specifically engineered to work with the lighter's unique design, ensuring a consistent and safe burning experience.