The conversion of low-grade fossil and biogenic energy resources to a high-quality chemical energy carrier (syngas) in a high-pressure entrained flow gasification process opens a wide spectrum for energy efficient fuel conversion. Typically, twin-fluid atomizers are used to generate fuel spray in high-pressure entrained flow gasification. The quality of the syngas produced by entrained flow gasifiers depends strongly on drop size distribution generated by the burner nozzle. In consequence fundamental knowledge concerning the influence of operating parameters, especially ambient pressure on spray quality, is mandatory. Atomization experiments were performed using an external-mixing twin-fluid atomizer and varying reactor pressure up to 21 bar. Radial SMD profiles were measured using a phase Doppler analyzer. Additionally, primary jet breakup was investigated using a highspeed camera. To qualitatively prove the PDA results a photo-optical shadowgraphy system was used to estimate the size range of the droplets. The experiments showed that keeping the We number constant while varying ambient pressure leads to an increase of SMD with increasing ambient pressure. Keeping the gas velocity constant resulted in constant SMD values nearly independent from ambient pressure. The conducted analysis of experimental data shows that the typically used dimensionless parameter, the We number, for prediction of droplet size is not favorable for correlations to be valid in a wide range of reactor pressures. Finally the results were used to generate a semi-empirical model for prediction of SMD, based on a simplified theoretical energy consideration.