A method for producing a butanol gasoline blend having good cold start and warm-up (CS&W) driveability performance comprising: (a) providing at least one biologically-sourced butanol isomer obtained through fermentative production; and (b) blending said isomer with gasoline to form a butanol gasoline blend, the butanol gasoline blend having a specific ASTM D4814-09b Table 1 vapor pressure / volatility class; (c) determining a high butanol driveability index (HBDI a) value for the butanol gasoline blend by the linear combination BuOH(A 1 + A 2 E200 + A 3 RVP); wherein BuOH is the concentration in volume percent of the at least one biologically-sourced butanol isomer in the butanol gasoline blend; E200 is the volume percent of the butanol gasoline blend that distills at temperatures up to 200°F [93.3°C]; RVP is the Reid Vapor Pressure in psi [or in kPa/6.89]; and A 1 is about 100.2; A 2 is about -1.5; and A 3 is about -2.4; when the at least one biologically-sourced butanol isomer concentration is up to 70 volume percent and wherein the total weighted demerits of the butanol gasoline blend is less than 40; and (d) adjusting the amount of gasoline and/or the amount of the at least one biologically-sourced butanol isomer such that the value of HBDI a is below the maximum limit for driveability index for the specific class of gasoline as specified in Table 1 of ASTM D 4814-09b. (a) providing at least one biologically-sourced butanol isomer obtained through fermentative production; and (b) blending said isomer with gasoline to form a butanol gasoline blend, the butanol gasoline blend having a specific ASTM D4814-09b Table 1 vapor pressure / volatility class; (c) determining a high butanol driveability index (HBDI a) value for the butanol gasoline blend by the linear combination BuOH(A 1 + A 2 E200 + A 3 RVP); wherein BuOH is the concentration in volume percent of the at least one biologically-sourced butanol isomer in the butanol gasoline blend; E200 is the volume percent of the butanol gasoline blend that distills at temperatures up to 200°F [93.3°C]; RVP is the Reid Vapor Pressure in psi [or in kPa/6.89]; and A 1 is about 100.2; A 2 is about -1.5; and A 3 is about -2.4; when the at least one biologically-sourced butanol isomer concentration is up to 70 volume percent and wherein the total weighted demerits of the butanol gasoline blend is less than 40; and BuOH is the concentration in volume percent of the at least one biologically-sourced butanol isomer in the butanol gasoline blend; E200 is the volume percent of the butanol gasoline blend that distills at temperatures up to 200°F [93.3°C]; RVP is the Reid Vapor Pressure in psi [or in kPa/6.89]; and A 1 is about 100.2; A 2 is about -1.5; and A 3 is about -2.4; when the at least one biologically-sourced butanol isomer concentration is up to 70 volume percent and wherein the total weighted demerits of the butanol gasoline blend is less than 40; and (d) adjusting the amount of gasoline and/or the amount of the at least one biologically-sourced butanol isomer such that the value of HBDI a is below the maximum limit for driveability index for the specific class of gasoline as specified in Table 1 of ASTM D 4814-09b.