July 28 (Reuters) - Repsol SA CFO Miguel Martinez:
* Says $5.5 billion arbitration case with partner Sinopec has made the relationship between the two "increasingly complex and difficult"
* Says from an operational point of view, teams in both the North Sea and Brazil joint ventures continue working together and "delivering well"
* Says Repsol is "mindful of the interests of the joint ventures and will continue to honour all the commitments we have undertaken, and we expect Sinopec to do the same." Source text for Eikon: Further company coverage: (Reporting by Madrid Newsroom)