Plastic fuel tanks typically have a 10-15 year lifespan, supported by a 10-year warranty in the case of many major fuel and oil tank manufacturers. The lifespan of these containers can be affected by a wide number of factors, including the design (bunded tanks tend to outlast single skin tanks), conditions, and maintenance. Regularly maintained plastic fuel tanks can last for up to 20 years.
For those looking for a tank set to last over the 20-year mark, steel fuel tanks may be a safer bet. Though slightly pricier, steel tanks are generally less prone to age and environmental damage.