Growing pressure on businesses to disclose environmental information also implies an increase in the volume of such disclosures. This article is an attempt to present the guidelines and to assess the levels of environmental information disclosure in Bulgaria.Companies, which were identified as the most responsible for air pollution, are thermal power plants. We have studied only these, which produce electricity. A checklist, containing 17 environmental performance assessment criteria, was developed and was completed based on the information, disclosed in the companies' annual financial statements, their activity reports and their websites. Based on a comparative analysis of the quantitative and qualitative information, disclosed by examined companies, we discovered that most companies disclose quantity environmental information, largely neglecting qualitive information. Taking into account the character of their activity, they should disclose more environmental information, especially qualitive information.