Butanol is frequently discussed as a potential biofuel as it can be produced via acetone-butanol-ethanol (ABE) fermentation. Like ethanol, it can be added to conventional petrochemical fuels in order to reduce the use of fossil fuels. However, such blending of butanol is only possible if the effects upon mixing are understood. This study makes an important step towards developing detailed knowledge of the influences butanol may exert on a hydrocarbon based fuel. Infrared (IR) spectroscopy is employed to analyze the molecular interactions in the fuel blends. In a first step, binary mixtures of butanol and n-decane, which is utilized as a single-component fuel surrogate, are studied. In the second step, blends of butanol with commercial B5 diesel fuel are analyzed. The presence of n-decane weakens the hydrogen bonding interactions between the butanol molecules. When butanol is added to diesel, strong interactions with the biodiesel components containing ester groups are found. Moreover, the potential of using IR spectroscopy for the quantitative analysis of the blends is evaluated. It is shown that the spectra allow a very accurate measurement of the butanol content.