Petrol retailers have rejected any suggestion a third-party website listing petrol pump prices every 15 minutes enabled them to engage in price-fixing.
The competition watchdog claims five retailers - BP, Caltex and the fuel-selling arms of Coles, Woolworths and 7-Eleven - used their membership of the Informed Sources website to watch their competitors' prices.
The Australian Competition and Consumer Commission (ACCC) alleges this breaches consumer law, and has launched a Federal Court case against the five retailers.
ACCC counsel Michael O'Bryan QC said in a directions hearing before Justice Bernard Murphy on Friday that the Informed Sources site facilitated co-ordination and co-operation in the setting of prices by the petrol retailers, which was likely to lessen competition.
Neil Young QC, for Coles Express, said Informed Sources just provided "historical" information on petrol prices.
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"There certainly isn't (price-fixing)," Mr Young said.
The ACCC was suggesting better access to historical information would lead to the lessening of competition, he said.
Petrol retailers had always checked each other's prices, Mr Young said.
In days past, runners would be sent out to look at prices on petrol station boards, or someone local could be contacted by phone to provide the same information, he said.
Julian Burnside QC, for 7-Eleven, questioned whether knowing a competitor's prices necessarily diminished competition.
He said petrol retailers took into account all manner of things other than competitors' prices in setting their own prices.
Peter Brereton SC, for Caltex, told the court the ACCC was alleging competition was likely to be lessened, not that it had been lessened.
Counsel for the petrol retailers also expressed concern about the ACCC's definition of the market in which competition had allegedly been lessened.
In a Melbourne-wide market, for example, it was ludicrous to think a motorist would rush across town for a one cent per litre saving, Mr Burnside said.
Justice Murphy set another directions hearing for February 13, 2015, and the start of what may be a six-week trial was set down on September 7.
