Abu Dhabi National Oil Company (Adnoc) has signed a close-out agreement with the existing partners on its onshore oil fields, ending the 75-year partnership of the five international oil companies (IOCs).

Abu Dhabi will take full control of the fields after the existing Abu Dhabi Company for Onshore Oil Operations (Adco) joint venture officially expires on 11 January.

Meanwhile, Adnoc is assessing bids from at least 10 companies vying to form a concession to operate the assets, which is not expected to start until early 2015.

The current onshore concession, signed in the 1970s, is held by a joint venture of Adnoc and five IOCs: the UK’s BP; US-based ExxonMobil; UK/Dutch Shell Group; France’s Total; and Portugal’s Partex.

Adnoc’s leadership said late last year that these IOCs would assist it in operating the fields on a risk-free basis until a new partnership is formed.

With the exception of Partex, all the existing partners have lodged bids for a place in the new concession. Other bidders in the running include China National Petroleum Corporation (CNPC), Italy’s Eni, Japanese group Inpex, Korea National Oil Corporation (KNOC), US-based Occidental Petroleum (Oxy) and Norway’s Statoil.

The end of the concession was marked by an official closing ceremony in Abu Dhabi, which was attended by senior executives from Adco, Adnoc, the five IOCs and the Supreme Petroleum Council (SPC), which oversees energy policy in the emirate.

Abu Dhabi, the UAE’s largest emirate and the world’s third-biggest oil exporter, generates more than half of its crude output from its onshore fields.