We supply the secondary reference fuels of known high and low cetane numbers for measuring the ignition quality of diesel fuel as specified in ASTM D-613 for use in a CFR test engine. These fuels are used to obtain the interval between the start of injection and actual ignition of a sample diesel through the bracketing procedure detailed in the test method to determine its cetane number. Along with these, we also offer check fuels low and high for fit for purpose testing and checking engine conditions at one point only. Utilizing secondary reference fuels to determine cetane generally provides improved usability compared to using primary reference fuels. On average they are lower cost compared to primary reference fuels and as actual diesel fuel blends, have properties that potentially provide better ease of use and shelf-life stability.