The research work of the present study is focused on the detailed comparison of two external mixing twin fluid nozzle concepts: (i) a central liquid jet with annular gas stream, (ii) an annular liquid sheet with central gas jet. Both nozzle types are applied in high pressure entrained flow gasifiers (EFG), where atomization is characterized by low Gas-to-liquid ratio (GLR) and high fuel viscosity. In order to compare spray formation as well as atomization efficiency in terms of Sauter mean diameter, a nozzle with equal orifice area of the gas and liquid exit is investigated. The nozzle enables equal atomization conditions concerning GLR, liquid mass flow, velocity of liquid and gas, as well as momentum flow ratio for both nozzle configurations. 4 Newtonian liquids: water and three glycerol/water mixtures with viscosity of 1mPas, 50mPas, 100mPas and 200mPas are used for the experiments in both nozzle configurations at various GLR. For spray analysis, a high speed camera, a shadowgraphy system as well as a phase-doppler analyzer are applied. The use of three different measuring techniques allows for characterization of primary breakup as well as local drop size distribution. With the high speed camera the breakup regime morphology is detected and classified for both operating configurations. Radial measurements of the local Sauter mean diameter are conducted with the phase-doppler analyzer. Furthermore, the spray angle is detected and the integral Sauter mean diameters for all operating conditions is compared for both nozzle configurations to evaluate atomization efficiency.