NRG Flinders chief executive officer, Robert Althoff, also said politicians and regulators should stop tinkering with the market, which was working well and avoid "quick fixes" such as price caps and instead concentrate on providing a stable environment.

"The energy market is working - leave it alone," Mr Althoff said speaking at the South Australian Energy Market conference in Adelaide.

Mr Althoff also rejected claims that major users had been hit with significantly higher power contracts under the contestable market, saying some had enjoyed a decline of as much as 20% in real terms.

Last week, the offer price on the National Electricity Market for a megawatt of electricity from Queensland reached $9999.90, which was the first time the permitted maximum price level had been reached.

Another energy executive, Ed Metcalfe from International Power, which owns the Pelican Point power station in Adelaide, also called for an end to "casual tinkering" by regulators.

Such actions affected investment confidence in a market that was still maturing, Mr Metcalfe said.

He forecast more integration of generation and retailing to reduce market risk and volatility. While this would lead to fewer providers, there would be a greater range of competitive energy products, he said.