Actual pump prices will have to be displayed by service stations under a code of practice being introduced by the South Australian Government.

It wants to end any confusion from petrol sellers advertising discount schemes, rather than the full price.

Acting Premier John Rau said it would stop petrol retailers creating an impression their discounts applied for all customers.

"Anybody who wants to offer some sort of loyalty reward will be able to continue to do that," he said.

"We're not attempting in any way to interfere with that.

"What we are asking for though is absolute transparency in the price at the pump for any passerby."

Sorry, this video has expired SA moves against discount displays

New South Wales already has made such a change, which must be fully implemented by September this year, and Mr Rau said the new code would take effect in SA later in the year too.

"The price advertised on those large advertising boards outside petrol stations will be the charge for anybody driving into that station for petrol," he said.

"It's very important that when they're making that split-second decision 'Do I go in or do I not?' they are able to assess the actual price at the pump for them."

Motoring organisation the RAA has backed the Government's move.

Spokesman Chris West agreed the current system allowed retailers to misrepresent the pump price and could be confusing for motorists.

"Often the discounted price is the most prominent price on the billboard and at this stage many motorists do get misled by that price," he said.

Woolworths said it had received very few complaints about its display of discounted prices.

It said the price boards issue was being considered nationally and the SA Government should have waited until that process was complete.

Coles said it would comply with any change.

Independent fuel outlets said they were struggling to compete with discount schemes and such loyalty programs should be banned.