Traditional sustainability reporting is based on an internally developed methodology and does not fully cope with the sustainability performance evaluation, especially from an external perspective. This study aims to fill this gap by offering a tool that may be used to assess the company's performance based on the results presented to external users. For this purpose, a two-stage data envelopment analysis (DEA) is proposed, that enables a comparison of the sustainability performance disclosed in non-financial reports in the banking industry in Poland, Croatia, and Romania. The findings of our study identify differences between the efficiency of sustainability performance in the banking sectors of all three countries. The proposed approach to compare hard-to-compare sustainability performance may significantly contribute to the decision-making process for stakeholders and, therefore, to the advancement of sustainability performance measurement research.