The oil ministry has not yet given the green signal to explorer ONGC. The main reason behind this delay is that, there will be a meeting with top executives of Scottish explorer Cairn Energy Plc and NRI metals industrialist Anil Agarwal's London-listed Vedanta Resources.

They will have a discussion on their near-$10 billion M&A deal. This deal is the largest in the Indian oil sector so far.

The meeting will be held on this Sunday by the ministry. They will discuss issues blocking Vedanta Resources' bid to acquire Cairn India.

It is one of the Cairn Energy's Indian arms that operate the Barmer oilfield and other acreages in partnership with ONGC.

The ministry was unhappy with ONGC's explicit demand for an equitable royalty management for the Barmer fields, Cairn's crown jewel. In return they would be giving up pre-emption rights.

In Barmer fields ONGC has 30% equity however it pays 100% royalty due to a policy irregularity. For this reason, Barmer has been losing proposition for the state-owned firm.