Oil and Natural Gas Corporation (ONGC) is considering a rebid for acquiring PetroKazakhstan, a Canadian oil firm in Kazakhstan.Though PetroKazakhstan has already accepted a bid by China National Petroleun Corporation (CNPC), the deal is yet to be ratified by its shareholders.ONGC officials said today that since the EGM of PetroKazakhstan is scheduled for October 18, the company can make a revised offer before the meeting.CNPC had clinched the deal last month with a winning bid of $4.18 billion as against ONGC's offer of $3.98 billion.The committee of secretaries has already given the nod to ONGC Videsh, the overseas arm of ONGC, to make a counter bid.