This study tries to characterize the spray of compressed natural gas (CNG) and hydrogen under ambient conditions using Schlieren imaging technique and image processing. A comparative analysis of the tests is presented. Both wide and narrow cone angle injectors had been used to investigate the spray development and their behaviors at different injection pressure (1.2 to 1.8 MPa). It was found that the intensity of the injected gas for narrow angle injector was higher than wide angle injector before the time reached 5.0 m sec-1. Generally, both the penetration and cone angle show an increase with the increase of injection pressure. As for the spray of pure H2, the images showed that the spray spreads faster than pure CNG and the spray has also exhibited a larger cone angle due to the lower density of hydrogen relative to CNG. © 2011 Asian Network for Scientific Information.