Final answer:
A Dry gas seal is the best choice when oil leakage containment is essential for an oil-free product as they ensure no oil contaminates the process fluid.
Step-by-step explanation:
When oil leakage containment is critical for an oil-free product, the most appropriate type of seal to use is a Dry gas seal. These seals are designed to prevent oil from contaminating the process fluid, making them suitable for applications where purity is essential, such as in pharmaceuticals or food processing. Mechanical seals are also used to prevent leakage but might not offer the same level of oil-free assurance as dry gas seals. Oil-free packing rings might be used in some contexts but they are typically less effective than dry gas or mechanical seals in high-pressure systems, and Liquid film seals are not suitable for oil-free applications, as they inherently involve a liquid lubricant.