What if demand exceeds production? From which countries can CoOs then be bought?

Both GoOs and CoOs can be imported or exported, provided the country concerned is a member of the European Union (EU) or a signatory to the European Economic Area (EEA) Treaty. In addition, the country must be a member of the Association of Issuing Bodies (AIB), which oversees the standardised system: the European Energy Certificate System (EECS).