While ONGC did not provide details of the proposed restructuring, sources in the company said an advisor would be appointed to suggest possible options.
The board of the company will take a call on the options suggested by the advisor.
ONGC is looking at trimming down the structure by merging some of the subsidiaries.
While MRPL operates a 15 million tonnes a year refinery at Mangalore in Karnataka, HPCL has two refineries at Mumbai and Vizag. OPaL has built at Rs 320 billion petrochemical complex at Dahej in Gujarat, while ONGC Tripura Power Co Ltd (OTPC) operates a 726 MW power plant at Palatana in Tripura.
It also has two SEZ companies - Dahej SEZ Ltd and Mangalore SEZ Ltd. Also, it has a pipeline company in Petronet MHB Ltd and a stake in helicopter service operator, Pawan Hans Ltd as well as Petronet LNG Ltd.
Sources said while there is certainly a case for merger of MRPL with HPCL for not just business synergies but also help avoid penalties from market regulator SEBI for not meeting public float requirement in case of the former.
Also, some other units too can be combined.
In the regulatory filing, ONGC referred to the acquisition of government's stake in HPCL earlier this year as part of government's proposal to create a public sector 'oil major' which will be able to match the performance of international and domestic private sector oil and gas companies.
ONGC has in past spoken of benefits of bringing all refining business under one company. HPCL management too has supported taking over MRPL to create India's second-biggest public sector oil refining firm.
"The restructuring proposal shall safeguard the overall interest of the public shareholders of all ONGC group companies," ONGC said.
The restructuring, it said, would be done taking into account the need for better value creation and synergy among group firms. Also, it would be done to meet the minimum public shareholding requirement in case of MRPL.
SEBI's listing rules require a minimum public float of 25 per cent. In case of MRPL, the float is less than 11.5 per cent.
"The implementation of any such restructuring proposal shall be subject to the approval of the Government of India, the board of directors of the relevant companies and other stakeholders of such companies in terms of applicable laws," ONGC said.