© 2021 Elsevier LtdThe aim of this paper was to investigate the effects of n-butanol/gasoline blends (nBGBs), 2.5% n-butanol/gasoline blend with 9% water injection into the intake air on the engine performance, fuel cost and exhaust emissions in an automobile spark-ignition engine. Experiments have been performed for three different nBGBs, nB2.5 (nB2.5 contains 2.5% n-butanol and 97.5% gasoline in volume basis), nB5 and nB7.5 for five different loads at 3000 and 5000 rpms. The test results showed that nBGBs generally decrease brake specific fuel consumption (bsfc) at all of the selected operating conditions. The maximum reductions of bsfc at 3000 and 5000 rpms have been attained at the levels of 7.22% and 9.99% for nB2.5, respectively. nBGBs decrease carbon monoxide (CO) and total hydrocarbon (THC) emissions at the selected operating conditions. However, nBGBs increase nitrogen oxides (NOx) at 3000 rpm. At 5000 rpm, nB2.5 and nB5 reduce NOx but nB7.5 increases NOx. The NOx could not be reduced as much as desired by applying nBGBs. For this reason, 9% water introduction into the intake air with nB2.5 (nB2.5-WI9) have been applied to decrease NOx. The test results showed that nB2.5-WI9 and nB2.5 decrease NOx approximately 58% and 9%, respectively at 5000 rpm. nB2.5-WI9 reduces CO more than nB2.5 at two engine speeds. However, nB2.5-WI9 increases THC and bsfc more than nB2.5. Total fuel cost for nB2.5 and nB2.5-WI9 become higher than neat gasoline. However, nB2.5-WI9 shows higher fuel cost as compared to nB2.5.