In this study, gas entrainment characteristics of a diesel spray injected by a group of closely spaced two-orifices (group-hole nozzle) were investigated. Both free and wall-impinging sprays were considered. The gas entrainment characteristics of the group-hole nozzle spray were compared to those of single-hole nozzle sprays: one has the same total hole area with the group-hole nozzle, and the other has the same hole diameter. The gas entrainment characteristics of diesel sprays were investigated using a particle image velocitmetry technique coupled with a laser induced fluorescence technique (LIF-PIV technique). The spray tip penetration of the group-hole nozzle was the shortest among the applied nozzles in a free spray condition, while it was the longest in a wall-impinging condition. In the free spray condition, the gas entrainment of the spray was enhanced by the group-hole nozzle due to extensive momentum exchange with surrounding gas and superposed gas entrainment motion of the two-jets injected by the group-hole nozzle. After wall-impingement, the group-hole nozzle spray showed a stronger wall-jet vortex and increased gas entrainment compared to the single-hole nozzle sprays due to enhanced spray/wall interaction caused by the momentum interaction of the two-jets from the group-hole nozzle. Asymmetric shape of the group-hole nozzle spray resulted in an asymmetric gas velocity distribution of the spray both in the free and wall-impinging conditions. (C) 2010 Elsevier Ltd. All rights reserved.