This paper motivation is to introduce a few guidelines of a model in search for a conceptual framework for sustainability reporting. We are presenting the levels of information reliability witch are derived mainly from accounting conceptual frameworks, and Global Reporting Initiative (GRI) Guidelines. As the study methodology we are using an inductive approach: we analyze the qualitative characteristics of specific environmental indicators, in order to assess the degree of relevance and reliability of each particular provision. We will finally make an attempt to derive the objective of sustainability reporting, while evaluating the degree of usefulness of this type of documents that closely follow the more formalized process of financial reporting. We conclude that there are a number of reasons for not reporting; most of these are related to internal data reliability. Hence, stakeholders cannot distinguish between different types of data unreliability; and the GRI does little on this matter.