There's no shortage of facts and figures about the growth (or lack of growth, depending how you read the numbers) of open access publishing. A recent post on the Imaginary Journal of Poetic Economics blog presets an impressive array of data and milestones. But the European Commission is looking for a more sustainable way of measuring OA. It has published a call for proposals for a study to develop a set of indicators to measure open access. The aim is for monitoring of the growth of open access literature from 2000 onwards within the European Research Area (ERA) and beyond. The EC sees OA as a key part of the "single market for research and innovation in which researchers, scientific knowledge and technology circulate freely."