TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: In the method (M1), the butanol gasoline blend comprises up to 27 vol.% of the biologically-sourced butanol isomer, and the renewable components of the butanol gasoline blend are maximized while good driveability performance are maintained; the blend comprises ethanol (up to 15 vol.%); and the total concentration of ethanol and the biologically-sourced butanol isomer is less than 30 vol.% of the blend. The method (M1) further involves blending a sufficient volume of light hydrocarbons to adjust the value of LBDI below the maximum limit for DI. The method (M2) further involves blending a sufficient volume of light hydrocarbons to adjust the value of Eff100 above the minimum limit for E100. In the method (M3), the total weighted demerits of the blend are less than 15. The method (M3) further involves determining the LBDI before blending the gasoline, the biologically-sourced butanol isomer, and optionally ethanol to form the blend; determining the LBDI after blending the gasoline, the biologically-sourced butanol isomer, and optionally ethanol to form the blend; and optionally, adjusting the gasoline amount, the biologically-sourced butanol isomer amount and/or the ethanol; and determining the LBDI during blending the gasoline, the biologically-sourced butanol isomer, and optionally ethanol to form the blend; and optionally, adjusting the gasoline amount, the biologically-sourced butanol isomer amount and/or the ethanol, so that the LBDI has a value equal to the linear combination (c1) below the maximum limit for DI for the specific class of gasoline. Preferred Components: The biologically-sourced butanol isomer is isobutanol. Preferred Blend: The blend further comprises a sufficient volume of light hydrocarbons to adjust the value of LBDI below the maximum limit for DI. Preferred Definitions:    a1=1.5;    a2=3;    a3=1;    a4=2.4;    a5=16;    a6=0.3;    b1=2.3;    b2=0.034.    Provided that: when the ethanol concentration is less than 10 vol.%, then a1 is 1.5, a2 is 3, a3 is 1 and a4 is 2.4; when the biologically-sourced butanol isomer concentration is less than 20 vol.%, then a5 is 16 and a6 is 0.3; and when the biologically-sourced butanol isomer concentration is less than 20 vol.%, then b1 is 2.3 and b2 is 0.034.    EXAMPLE - No suitable example is given.