NOVELTY - Producing (M1) a butanol gasoline blend involves: providing at least one biologically-sourced butanol isomer; and blending the isomer and optionally ethanol with gasoline to form the blend, where the blend has vapor pressure corresponding to a specific ASTM D4814 vapor pressure/distillation class of gasoline. The blend has a value of low butanol driveability index (LBDI) equal to specific linear combination below maximum limit for Driveability Index (DI) for specific class of gasoline. The total weighted demerit of butanol gasoline blend is less than 40.    USE - For producing butanol gasoline blend (claimed), which is useful as fuel in a spark-ignition engine.    ADVANTAGE - The process produces the oxygenated butanol gasoline having good cold start and warm-up driveability performance.    DETAILED DESCRIPTION - Producing (M1) butanol gasoline blend involves: providing at least one biologically-sourced butanol isomer; and blending the butanol isomer and optionally ethanol with gasoline to form a butanol gasoline blend having a vapor pressure corresponding to a specific ASTM D4814 vapor pressure/distillation class of gasoline. The butanol gasoline blend has a value of low butanol driveability index (LBDI) equal to the linear combination a1T10+a2T50+a3T90+a4EtOH+BuOH(a5-a6 E200) (c1) below the maximum limit for Driveability Index (DI) for the specific class of gasoline, where e maximum limit for DI for the specific class of gasoline is specified in Table 1 of ASTM D 4814-08a. The total weighted demerit of the butanol gasoline blend is less than 40.    T10=temperature for distillation of 10 vol.% of the butanol gasoline blend;    T50=temperature for distillation of 50 vol.% of the butanol gasoline blend;    T90=temperature for distillation of 90 vol.% of the butanol gasoline blend;    EtOH=concentration in volume percent of ethanol in the butanol gasoline blend;    BuOH=concentration in volume percent of at least one biologically-sourced butanol isomer in the butanol gasoline blend;    E200=volume percent of the butanol gasoline blend that distils at temperatures up to 200 degrees F;    a1-a6=coefficients selected to give a substantially linear relationship between the values of the linear combination for the butanol gasoline blend containing at least one butanol isomer and optionally ethanol and the logarithms of the mean corrected total weighted demerits from test measurements of (CS and W) driveability performance for such blends, at concentrations of ethanol less than 20 vol.%, at concentrations of at least one biologically-sourced butanol isomer less than 30 vol.%, and at total concentrations of ethanol and at least one biologically-sourced butanol isomer less than 35 vol.%.    INDEPENDENT CLAIMS are included for the following: 1) a method (M2) for producing the butanol gasoline blend involving: providing at least one biologically-sourced butanol isomer; and blending the butanol isomer and optionally ethanol with gasoline, to form a butanol gasoline blend, where the butanol gasoline blend has a vapor pressure corresponding to specific EN228 volatility class of gasoline, and an Eff100 value equal to the linear combination E100-BuOH(b1-b2E100) above the minimum limit for E100 for that class of gasoline as specified in Table 2 of EN228, where the total weighted demerits of the butanol gasoline blend is less than 40; 2) a butanol gasoline blend having good cold start and warm-up (CS and W) driveability performance comprising either: a suitable amount of the biologically-sourced butanol isomer and optionally ethanol blended in gasoline; or a blend of a specific EN228 volatility class of gasoline, biologically-sourced butanol isomer, and optionally ethanol; and 3) a method (M3) of identifying a gasoline blend involving: blending gasoline with butanol, and optionally, ethanol; measuring fuel variables E200, T10, T50, and T90; inputting the fuel variables in equation (c1) to calculate a LBDI of the butanol gasoline blend; and comparing the LBDI to a maximum limit for DI for the specific class of gasoline, where the blend has good cold start and warm-up driveability performance if the LBDI is below the maximum limit for the DI for the class of gasoline specified in Table 1 of ASTM D 4814.    BuOH=concentration in volume percent of at least one biologically-sourced butanol isomer in the butanol gasoline blend;    E100=volume percent of the butanol gasoline blend that distills at temperatures up to 100 degrees C;    b1 and b2=coefficients selected to give a substantially linear relationship between the values of the linear combination for the butanol gasoline blends containing at least one butanol isomer and optionally ethanol and the logarithms of the mean corrected measured total weighted demerits for such blends, at concentrations of ethanol less than 20 vol.%, at concentrations of the biologically-sourced butanol isomer less than 30 vol.%, and at total concentrations of ethanol and biologically-sourced butanol isomer less than 35 vol.%.