Australia's levels of market concentration leave consumers worse off and a new approach is needed, the Australian Competition and Consumer Commission (ACCC) chairman has warned.

Key points: Australia has outpaced the US in big business market share growth

Australia has outpaced the US in big business market share growth Top 100 listed companies now account for almost half of GDP

Top 100 listed companies now account for almost half of GDP Groceries, gambling, super, banking, telecommunications and energy are biggest areas of concern

Rod Sims said the revenue of Australia's top 100 listed companies had surged from 27 per cent of GDP in 1993 to nearly 50 per cent GDP in 2015, meaning Australian big business growth outpaced even the United States.

"What we've really got to make sure is there's adequate competition to see any benefits from scale flow through to the general economy," he said.

Mr Sims said the ACCC was concerned about big businesses increasingly using arguments that heavy concentration within industries was not a concern, which Mr Sims said "basically defy conventional economic wisdom".

"Conventional economic wisdom says monopolies will charge more and give less, it says that highly concentrated markets with high entry barriers are going to see consumers worse off," he said.

"And yet we're seeing that conventional economic wisdom often turned on its head and really putting the ACCC in a position of having to prove conventional economic wisdom."

Only 29 of the companies in the ASX 100 in 1990 are still there, mostly because of mergers. ( Supplied: ACCC, Port Jackson Partners )

Mr Sims said in Australia the onus was on the ACCC to prove whether a merger was anti-competitive, while in the United States the onus was placed on the merger parties.

He said in the US when a company sought a merger, the general presumption was that the merger would be anti-competitive with higher levels of concentration.

"And the presumption shifts to the merger parties to prove why this is the exception to the rule and the economic wisdom and it's good for the economy," he said.

Mr Sims said, while an approach such as the US's would probably need to be enshrined in legislation to succeed in Australia, he said there was room to start the conversation.

Australia needs to 'hold the line' against further mergers

Mr Sims said Australia was at a "tipping point" and that it would become problematic if the country found itself with more concentration.

"If we can sort of hold the line here, then we should be ok," he said.

Mr Sims said it was important to note that there are many once-dominant firms that had been challenged.

"The supermarket sector for example, Aldi coming in has made a huge difference to benefit consumers," he said.

"So the more we can lower entry barriers and see new competitors come in the less concerned we are."

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Mr Sims said the sectors of the economy that concerned him and had the highest levels of concentration were groceries, gambling, superannuation services, banking, broadband and telecommunications.

He also said that energy had it "in a sense".

"So all key sectors, but right now it's sort of ok," Mr Sims said.

"We've got four different broadband players that do have different value propositions and so probably are competing, but you wouldn't want that four to go to three.

"The other point you've got to watch out for is that the big guys don't keep eating up the new start-up companies."

Editor's note: The ACCC has corrected the figures it initially released on market concentration, which original said the top 100 listed companies accounted for 15 per cent of GDP in 1993.