Table 9.2.4 illustrates the blending octanes of various polymer gasoline fractions when blended with different base stocks. The reference base stock was a mixture of approximately 60% FCC gasoline and 40% reformate, having a clear octane of 93 RON and 80.8 MON. Blend stocks consisting of the various polymer gasolines were added at 10 or 20 vol% levels and the blending octanes were back calculated from the octanes measured in the resulting mixtures. It must be noted, however, that small errors in the determination of the octane values can lead to significant fluctuations in the estimation of the blending octanes.