Dr Anthony Asher, the convenor of the Actuaries Institute's retirement incomes working group, said only people on old-style defined benefits superannuation schemes were guaranteed an income until they died.

The federal public service moved from a defined benefits superannuation scheme to a defined contributions scheme in 2005.

While it will be many years before public servants start retiring under the new arrangements it is an issue they need to be mindful of as they make fund decisions and retirement plans over the course of their working lives, he said.

A report released by the institute on Thursday found a growing number of Australians were at risk of using up all of their superannuation before they die.

"A significant minority of retirees have, in recent years, run out of retirement savings before death," Dr Asher said.

"We need to understand why some people appear to be spending too much and what happens when the money runs out. It could be intentional as their income needs decline such that the old age pension is sufficient [or] it could be because they have lost money due to dementia, financial abuse or poor decision making."

The study indicated most people were careful in the way they managed their super savings after retirement. There was no evidence any significant number of superannuants were spending their nest eggs to qualify for the pension.

"What is apparent is that even when they are careful some people do outlive their investments," Dr Asher said.

"Reasons for this can include just living a very long time or having an unrealistic expectation of what the yield from their superannuation will be."

The report found 20 per cent of superannuants aged between 75 and 85 were drawing down 10 per cent or more of their principal a year, an amount Dr Asher described as "unsustainable" in view of their probable life expectancy.

"People in this age bracket are almost all fully retired and we assume they are drawing down a regular amount more than the minimum because they are using it for spending," he said.

"Their spending will have to decline fairly quickly over time or they will run out completely and face a drop to the old age pension."

Dr Asher, an associate professor at the University of NSW, said while compulsory superannuation was a good concept it could be fine tuned to work better.

"There is a need to review the types of annuities that can be sold by super funds to allow higher risk, higher yield investment options to be brought into the market," he said. "There is also a need for longevity insurance, the opposite of life insurance, to cover people against living longer than they had expected or budgeted for."

With an annuity a superannuant can effectively live off their capital, freeing up money for other purposes such as helping their children into a home.