Petrol retailers are making their highest gross margins since the competition regulator began monitoring prices despite fuel prices hitting a 14-year low, indicating that they are not passing on the full benefits of lower global oil prices to motorists.

Releasing its latest report on the petroleum industry, Australian Competition and Consumer Commission chairman Rod Sims said he remained concerned about the petroleum industry's high gross retail margins.

The gross retail margin for petrol is the highest since the ACCC began monitoring prices in 2002. Credit:Bloomberg

The average price for petrol in the country's five largest cities was about $1.22 per litre in the year to June, the lowest annual average price in real terms since 2001-02.

However, gross retail margins rose by 1.2¢ per litre in the June quarter, and averaged 11.2¢ last financial year, making them the highest since the ACCC began monitoring prices in 2002.