The Irish Stock Exchange (ISE) has extended for a further five years its contract to use the Xetra electronic trading system developed by German stock market operator Deutsche Börse, the two companies announced on Thursday. ISE's contract had originally been scheduled to run until the end of this year, but the two sides agreed to extend the contract until 2010, they said in a statement. Financial details were not disclosed. Deutsche Börse, which operates the Frankfurt stock exchange, said that ISE would continue to use the British company CrestCo, a unit of Euroclear, for trade settlement, even though Deutsche Börse has its own rival clearing and settlement house, Clearstream. The move was significant in the context of the battle being waged between Deutsche Börse and arch-rival Euronext to take over the London Stock Exchange. The LSE is also a client of CrestCo and LSE manager and users want to continue to use CrestCo rather than Clearstream if a London-Frankfurt merger goes ahead. The ISE, CrestCo and Deutsche Börse have even agreed intensify cooperation by creating a Central Counterparty or CCP for the Irish market, the statement said.