According to documents lodged by lawyers Blake Dawson Waldron, with the Australian Stock Exchange, the Singapore company owns 840.2 million Optus shares, of which 751 million are from an early agreement between SingTel and Cable & Wireless, which has 52.5 percent of Optus.
SingTel has offered Optus shareholders three schemes worth about A$14 billion (S$13.2 billion).
On Friday, SingTel extended its Optus bid by a month, Dow Jones reported.
Australia's Foreign Investment Review Board has said it will take 90 more days to decide if it will give SingTel's takeover bid the green light.
The Age newspaper in Melbourne has reported that SingTel's bid for Optus will win federal government approval, "with the Defence Department agreeing to back the takeover after finalizing guarantees on the security of its satellite communications this week".
SingTel is 78 percent owned by the Singapore government.