It had in May applied to the Vietnamese authorities for a third extension of the exploration licence for deepsea Block 128 to maintain India's strategic interest in the South China Sea.
In a regulatory filing, ONGC said its overseas investment arm, ONGC Videsh Ltd (OVL) had applied for extension of block to PetroVietnam, Vietnam's national oil company, on May 28, 2015.
"In response of ONGC Videsh request, PetroVietnam has granted extension of the block up to June 15, 2016," it said.
The company has not found any hydrocarbon in the block but is continuing to stay invested.
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ONGC termed the extension as "routine" saying such an exercise is carried out in all the exploration blocks where extensions are required for further studies.
OVL first took a two-year extension of the exploration period till June 2014 and then another one year. That extended licence expired on June 15, 2015. The company has so far invested USD 50.88 million in the block.
OVL forayed into Vietnam as early as 1988, when it bagged the exploration licence for Block 06.1.
The company got two exploration blocks - Block 127 and Block 128, in 2006. However, Block 127 was relinquished due to poor prospectivity but the other Block 128 was retained.
The first extension followed China putting the area under Block 128 for global bidding.
China claims sovereignty over most of the South China Sea where Block 127 and 128 are located and had warned the Indian arm from drilling in the region.
OVL continues to own 45 per cent stake in Vietnam's offshore block 6.1 and its share of production was 2.023 billion cubic metres of gas and 0.036 million tonnes of condensate.