Woodside Petroleum's $US2.75 billion deal to buy Apache Corporation's liquefied natural gas interests is being scrutinised by the competition watchdog, which is studying whether it may affect wholesale gas supply and prices in Western Australia. The transaction, announced in December, would have Woodside take Apache's stake in Chevron's $US29 billion Wheatstone liquefied natural gas project in WA, as well as its interest in the Balnaves oil field in the Carnarvon Basin.