ONGC Videsh and it's subsidiary ONGC Videsh Vankorneft are said to have jointly signed definitive agreements with Rosneft, the Russian national oil company, for the acquisition of an additional 11 percent stake in JSC Vankorneft, the operator of the Vankor oil fields in East Siberia. ONGC Videsh had earlier acquired a 15 per cent stake in the Vankorneft on May 31. After the latest acquisition is complete, ONGC Videsh stake in Vankorneft will increase to 26 percent. The board of directors of both the companies and the governments of India and Russia will need to approve the deal. ONGC Videsh said in a statement that the transaction is expected to close by the end of the calendar year. Vankor is Rosneft's second largest field by production and accounts for 4 percent of Russian production. The daily production from the field is around 421,000 barrels per day of crude oil on an average and together with the earlier acquisition of 15 per cent, ONGC Videsh's share of daily oil production from Vankor will be about 110,000 barrels per day.