Hydrogen has many attractive intrinsic properties that can be used for improving engine efficiency and emission performance. In this paper, the presence and long term stability of hydrogen nanobubbles (HNBs) in gasoline fuel were investigated. A HNB-gasoline blend is fabricated by nanobubble generator which consists of gas-liquid dispersion system. After the generation of HNBs in gasoline, the presence and long-term stability of HNB in HNB-gasoline blend were experimentally examined by using the nanoparticle tracking analysis (NTA) method. The particle analysis was performed for 121 d at a constant temperature of 298.15 K. The results show that the mean diameter and concentration of HNB are 159.00 +/- 31.91 nm and 11.25 +/- 2.77 x 10(8) particles/ml, respectively, just after HNB generation in gasoline fuel. After 121 d of observation, there were no remarkable change in the mean diameter and concentration of HNB. From the results of gas chromatography/mass spectrometry (GC/MS) measurement, it is possible that some compounds in HNB-gasoline blend obtain functional group by replacement reaction and non-main component decreases. Furthermore, the zeta-potential of HNB-gasoline blend after 121 d was about -30 mV, indicating the existence and stability of HNBs in gasoline fuel for a long time. (C) 2015 Elsevier Ltd. All rights reserved.