Recent studies have shown that the use of highly premixed dual fuel combustion reduces pollutant emissions and fuel consumption in CI engines. The most common strategy for dual fueling is to use two injection systems. Port fuel injection for low reactivity fuel and direct injection for high reactivity fuel. This strategy implies some severe shortcomings for its real implementation in passenger cars such as the use of two fuel tanks. In this sense, the use of a single injection system for dual fueling could solve this drawback trying to maintain pollutant and efficiency benefits. Nonetheless, when single injection system is used, the spray characteristics become an essential issue. In this work the fundamental characteristics of dual-fuel sprays with a single injection system under non-evaporating engine-like conditions are presented. In particular, maximum liquid length and vapor penetration behavior of five blends of commercial gasoline and diesel were tested when injected through a single-hole nozzle into an optical engine under non-reactive conditions. The liquid and vapor penetration were determined with Mie scattering and Schlieren high-speed imaging techniques for different operating in-cylinder thermodynamic conditions and injection pressures. Experimental results confirm that the liquid length is increasing with the density of the blend and that injection pressure has little effect on the liquid length. A fuel with high density within the blends controls the liquid phase length. Blends with the higher gasoline volume percentage vaporize easily in relative terms. Experiments prove that the vapor penetration is a function of the momentum flux, therefore fuel density does not affect the vapor penetration.