Melbourne Airport makes the highest profit from parking but has the equal lowest consumer satisfaction level, a report Australia's competition watchdog has found.

Key points: Melbourne, Sydney had lowest consumer satisfaction

Melbourne, Sydney had lowest consumer satisfaction Melbourne parking profits up 22 per cent

Melbourne parking profits up 22 per cent Online booking for 'significant savings'

Online booking for 'significant savings' Rail link to have little impact on parking fees

The Australian Competition and Consumer Commission (ACCC) report examining airports in Brisbane, Sydney, Melbourne and Perth, found Melbourne's rating was satisfactory, which was equal lowest with Sydney.

"I think the disappointment there is we've seen quite a large increase in the revenue per passenger that the airports make and yet service levels over time, have been going backwards," ACCC chairman Rod Sims said.

"I think we'd like to see all airlines with a good rating."

Airports in Brisbane and Perth were rated good for their quality of service.

Melbourne Airport is investing $484 million on the construction of a new passenger terminal, which Mr Sims said should improve the problem with customer satisfaction.

"Hopefully things addressed by the very large investment nearly half a billion in new domestic terminal. That could address issues of aerobridge and customers' access to check-in facilities," he said.

Online booking key to cheaper parking at Melbourne Airport

Parking revenue at Melbourne Airport rose nearly 22 per cent to $108 million from 2014 to 2015, a profit of 73 cents from every dollar.

But the report found one way to make "significant savings" on the high cost of airport parking was to book online.

"We found savings of up to two-thirds you could make by booking online," Mr Sims said.

"That's probably at the higher end of the savings you could make but we were very surprised when we started looking at what you pay if you drive up versus what you pay if you book online."

Melbourne rail link would have little impact on parking fees

The report also examined the plan for a Melbourne rail link and Mr Sims said it found the market "segments in a very interesting way".

He said it found the main benefit of the train was that people would switch from other forms of transport, such as a taxi or train.

"It probably wouldn't affect the airport's market power in relation the parking," he said.

"It would affect it a bit, but not that much."

The report found passenger traffic in Melbourne was up 3.6 per cent in 2015 to 32.2 million, the largest increase of all of the four airports surveyed.