Prime Minister Scott Morrison has put the competition watchdog on notice over rising fuel prices.

The cost of petrol has been rising across the nation, with prices in Melbourne hitting a 10-year high last month, and Adelaide motorists forking out an average of $1.67 a litre as of Monday.

"I want some answers out of the ACCC," Mr Morrison told K Rock 95.5 on Monday.

"They're the cop on the beat, they're the ones we fund to go out there and monitor why prices are moving up and down and how they're timed."

The prime minister concedes some factors, such as the international cost of oil, are out of the local market's control, but said the ACCC had powers to investigate if consumers were being hard done by.

"What we can ensure is the people who are selling it here behave," he said.

"I'm expecting some action."

As treasurer last December, Mr Morrison directed the ACCC to monitor prices, costs and profits relating to petroleum products and services in Australia over two years.