CNG cylinders are the most important, dangerous, and expensive part of a CNG setup. The natural gas inside a CNG system is generally pressurized to 3000 or 3600 psi, depending on the model year (3600 on newer models which is different than the world standard and raises part costs, but we won't go there). Cylinders are designed to be extraordinarily strong and safe, but incorrect installation or using a tank past its expiration date could lead to disaster.

Additional tanks can be installed to extend a vehicle's range. However, cylinders should be installed by a professional and inspected for expiration date and any sort of damage (to the level of scratches). An expiration date should be listed on every CNG cylinder. Cylinders cannot be hydrostatically recertified because of high and frequent pressurization. An eBay search yields used 5-6 GGE tanks selling around $500-600.

Cylinders should be visually inspected by a CSA Certified CNG Cylinder Inspector every 3 years, 36,000 miles or after an accident of fire, which ever comes first - although no one currently appears to be enforcing this law in conjunction with smog or other inspections.

• (CA, Pomona) Structural Composites Industries
• (CA, Riverside) Luxfer Gas Cylinders
• (NE, Lincoln) Lincoln Composites
• (UT, Brigham City) HyPerComp Engineering Inc