Fancy a free shop fitout or six months rent free?

They are just some of the sweeteners being offered up to potential tenants looking for office space in Brisbane as landlords battle one of the toughest commercial markets in years.

High-rise buildings that once leased out at $1,200 per square metre are now going for $400 less.

The Property Council's latest figures put Brisbane's commercial vacancy rate at 15.3 per cent, down from 16.9 per cent six months ago.

Perth has the nation's highest number of empty office space at 22.5 per cent.

Blocksidge Real Estate's Jonathan Blocksidge said some of the challenges going on at the moment were "almost unprecedented".

Mr Blocksidge said some offices are not being rented at all. ( ABC News: Lexy Hamilton-Smith )

Mr Blocksidge said some landlords were angry or confused as to why they could not get the high rental yields they had been used to in the past.

"Some landlords say, 'I do not understand what is going on here, it has always been this much and I have always got an increase. And you want me to take a decrease? That is not something I want to accept'," Mr Blocksidge said.

He said some offices were not being rented at all.

"Some spaces or buildings have sat unloved and unoccupied for years," he said.

"Or it can be longer than two years."

Six-month wait between inquiries for office space

Right across the city, scores of offices are empty following the collapse of the mining boom.

The State Government's move to 1 William Street also put several office buildings back into the pool, with high vacancy rates being driven by lower demand but an increasing supply of stock.

The investigation found only one quarter of contracts were properly disclosed. ( ABC Radio Brisbane: Jessica Hinchliffe )

Cushman and Wakefield property specialist Leah Ong said it was definitely a "tenant favourable market", with free rent or 35 per cent incentives being offered by smart landlords as tenants get to dictate their terms.

She mentioned one example in the Riverside Centre where a tenant was saving $250,000 over five years after negotiating a fitout/rental package.

"It is tough. The mining collapse did hit Queensland hard and recovery is quite slow," she said.

Raine and Horne commercial agent Hudson Dale said it could be six months between inquiries for office space at present.

"It can be that ugly. In the city fringe it is a bit of a bloodbath," Mr Dale said.

Rents in areas like Lutwyche are lower at around $250 per square metre.

"For the rent to come down even 20 per cent to 30 per cent it is a hard pill for some of these guys to swallow," he said.

"And if they have decent money borrowed on the asset it is tough."

Suburbs also flush with office space

It is a sluggish market in the suburbs too due to the volume of apartments with office space downstairs coming online.

University of Queensland economist Professor John Foster said mixed-use developments did not always attract commercial tenants.

"I think there is a town planning misjudgement there," he said.

One expert said mixed-use developments do not always attract commercial tenants. ( ABC News: Lexy Hamilton-Smith )

"We have some cases in the UK where the retail section of buildings have never really prospered."

Mr Blocksidge said landlords needed to take a reality check in the tough economic climate.

"When one is challenged in business one looks for better, smarter, cheaper ways of going about things," he said.

"And of course negotiations with landlords fall into that category of a better deal.

"It can be a long time between drinks."

The Property Council's next set of data on vacancy rates is due out in July.