Origin Energy made the off market bid in July to acquire all the ordinary shares in OCA that it does not already own with the $4.25 offer.

Origin already held 85.23% of the 117 million OCA shares on issue and Origin executive director, commercial Bruce Beeren said the move was an attempt to tie up loose ends.

"85% ownership is neither here nor there when it comes to ownership so we basically wanted to confirm our position."

Under a pre-bid agreement with Santos Ltd, Santos has agreed to accept the offer in respect of 2.9 million shares, giving Origin a relevant interest in 87.69% of the issued capital. Origin has held a majority share in OCA since the mid 80s.

Apart from Santos' commitment for 2.9 million OCA shares, the Santos Group holds a further 11.8 million shares in OCA, which have now been committed to sale.