In response to Asdal’s (2011) call for studies of accounting numbers and authority, the present work studies how sustainability accounting numbers achieve authority in company-investor relations. Thereby, the study aims to further develop the literature’s explanation of accounting numbers’, and in particular sustainability accounting numbers’, authority. The study does so by analysing three conditions that contribute to quantitative techniques’ seemingly objective character and thus their ability to lend authority, according to Porter (1992a, 1992b, 1995). The study finds that the investor analysts’ familiarity with the sustainability accounting issues, the system and practice, rather than what the numbers seek to represent, allowed them to question the authority of the accounting numbers. Most frequently, the investor analysts questioned the use of sustainability accounting concepts. Rather than responding with further numbers, the corporate executives addressed such questioning by further describing and explaining their work, more or less successfully.