A process for controlling the composition of an xBOB so that the xBOB will yield an oxygenate-containing gasoline which precisely meets desired specifications when mixed with the desired amount of oxygenate. The process involves blending a plurality of blendstocks to produce an xBOB, withdrawing a sample of the xBOB, obtaining spectroscopic measurements for the sample, applying mathematical models that were based on correlation of xBOB spectra to associated oxygenate-containing gasoline properties, to predict laboratory analysis results for oxygenate-containing gasoline properties, and using the analysis results to control and optimize the blending process.