Various studies investigate the design of corporate sustainability reporting in light of institutional theory. Whereas most of this literature examines the external factors that influence sustainability reporting, few studies focus on the internal drivers of sustainability reporting, especially the role of environmental orientation. This paper attempts to address this research gap by comparing companies with differences regarding environmental orientation. Therefore it distinguishes between companies that prioritise sustainability as business goals (Emerging Davids) and companies that use sustainability goals supplementary to their core business goals (Greening Goliaths). The paper finds differences in the sustainability reporting guidelines used by Emerging Davids and Greening Goliaths. Greening Goliaths are more likely to report according to the guidelines of the Global Reporting Initiative than Emerging Davids are. Thereby the study leads to the assumption that Greening Goliaths react more strongly to institutional pressures in terms of sustainability reporting than Emerging Davids do. This paper applies institutional theory in the context of environmental orientation and provides first insights into different institutional pressures within this field. While institutional pressures strongly influence the sustainability reporting of Greening Goliaths, they have less impact on the sustainability reporting of Emerging Davids.