Indonesia announced last year that Pertamina would take over operation of the Rokan block, on the island of Sumatra, from oil major Chevron when its contract expires in 2021.
The move comes as President Joko Widodo pushes for the country to have more control over its natural resources.
Dwi Soetjipto, the head of the SKK Migas regulator, declined to give further details when speaking to reporters late on Thursday.
An energy ministry spokesman confirmed the signing, but did not give further details. Pertamina officials declined to comment.
Pertamina has estimated its capital expenditure on Rokan will reach around $70 billion over the 20-year life of its contract.
Pertamina last year estimated that Rokan would help it cut its crude imports by around 100,000 barrels per day (bpd) from about 400,000 bpd.
PT Chevron Pacific Indonesia, a unit of Chevron, lifted 195,753 bpd from the block in January-April, compared to a target of 190,000 bpd.
