Alcohol components are illegally mixed with petroleum products for tax evasion purposes, but this degrades vehicle performance. The alcohol content in petroleum fuel can be analyzed by gas chromatography. However, this technique requires a long analysis time and is expensive. $CrO_3$, also known as Jones reagent, changes color upon reaction with an alcohol. In this study, therefore, we analyze alcohol contents in vehicle fuel by using $CrO_3$ aqueous solution.