He told PIN buy-back deals were much more attractive due to their flexible nature. Ramezani said buy-back contracts can accelerate gas projects in the country. Buy-back deals have become the standard contract for foreign investors wanting a cut of the world's second biggest oil and gas reserves. Under these agreements, foreign firms operate Iranian oilfields for a period of about seven years and are compensated for their investment with a share of output. The state then repurchases the field. Some buy-back deals have gone sour for Iran.