Fuel Quality

The Weights and Measures Program is statutorily charged with assuring that petroleum products such as gasoline and diesel fuel, offered or exposed for sale in the State of Montana , meet the nationally recognized American Society of Testing Materials (ASTM) standards. For gasoline, the standard is D-4814 and for diesel, D-975. Testing for compliance to these standards is done by periodically sampling fuel products and sending them to an independent laboratory for analysis.

Another large component of fuel quality is that of octane content. In Montana, as in most other states, there are usually three grades of gasoline offered for sale, regular unleaded, mid-grade or plus, and premium or super, the difference between the three being the octane rating and corresponding price differentials. (The higher the octane rating, the higher the price)

When testing for octane in the field the bureau uses a Near-Infrared (NIR) octane analyzer, which will provide reproducible and repeatable results when calibrated against known standards. In Montana and other jurisdictions that use this technology, these portable analyzers are used as a screening tool to determine if a sample should be submitted to an accredited lab for further analysis of the octane content. Using this portable analyzer allows the bureau to screen far more fuel samples in less time and at a considerable cost savings than if all of the samples were submitted to a lab for testing.

In 1994, prior to the inception of the current octane testing program, a survey was done of over 200 fuel samples collected across the state. When tested for octane content, approximately 17 % were off- grade or had a true octane rating of less than that listed on the pump. Due primarily to the testing of octane by the bureau, this rate of off -grade fuel has dropped to 1-2% for the last three years (2002 - 04) which is consistent with other state jurisdictions that have a fuel quality program in place.

For additional information concerning octane, please see the Frequently Asked Questions.