The Athens and Istanbul bourses announced yesterday a joint index aimed at increasing liquidity in both equity markets. The largest 15 stocks from each market will participate in the index, based on their market capitalization, with the number of banks from each market limited to four. «We believe the common index will provide additional choices to investors in the two markets and facilitate cross-border access between the exchanges,» said Spyros Kapralos, chairman of the Athens bourse, in a statement. Calculated and maintained by STOXX, the Greece and Turkey 30 Index (GT-30), will have its composition reviewed twice a year. It will also be reviewed four times a year regarding capping factors, which assess the weight given to each share on the index. Istanbul Stock Exchange Chairman Huseyin Erkan said the GT-30 index will boost visibility for both markets and that the launch of the index «is a further step in our close cooperation with the Athens Exchange.» The new index follows a common trading platform the Athens bourse launched in 2006 with the Cyprus Stock Exchange. In July, the two exchanges broadened their cooperation, allowing Cypriot members access to the Greek derivatives market in a move that paves the way toward cheaper exchange of market data.