Australia's competition watchdog Thursday raised concerns about energy giant Royal Dutch Shell (Xetra: R6C1.DE - news) 's purchase of Britain's BG Group (LSE: BG.L - news) , saying it could raise domestic prices, while delaying a final decision to November.

The planned £47-billion (US$72.8 billion) deal announced in April has to be approved by the Australian Competition and Consumer Commission (ACCC) as well as Chinese regulators, and would make Shell (LSE: RDSB.L - news) the world's second largest oil and gas company.

But Commission chairman Rod Sims said the takeover could see Anglo-Dutch titan Shell direct the gas reserves of Australian firm Arrow Energy -- which it has a 50 percent interest in -- to BG's liquefied natural gas (LNG) facilities in Queensland state.

This would then remove some or all the gas from the local market to meet BG's contracts to supply LNG export markets, Sims added.

"Currently, Arrow has the largest quantity of uncommitted gas reserves in eastern Australia and there are a limited number of other potential suppliers to the domestic market," Sims said in a statement.

"If the proposed acquisition resulted in less supply of gas to the domestic market, therefore, this could substantially lessen competition to supply domestic gas users and lead to higher domestic prices and more restrictive contractual terms."

The ACCC was originally due to release the final decision in early September, but said it was now inviting further submissions from the industry and deferred an announcement until November 12.

Energy producer BG Group is developing Queensland Curtis LNG (QCLNG) through its Australian arm QGC, with the company claiming a world first at turning gas from coal seams into LNG.

The Shell-BG Group acquisition is the energy sector's biggest in a decade and consolidates the two firms' positions as the industry battles with sliding oil prices.

The deal was approved earlier this month by the European Commission, which said it did not raise competition concerns