South Australian MPs have spoken out about the challenges of voting on the voluntary euthanasia bill which will be introduced in Parliament tonight.

Key points: Voluntary euthanasia is not legal anywhere in Australia

Voluntary euthanasia is not legal anywhere in Australia SA has introduced 15 bills over two decades trying to legalise it

SA has introduced 15 bills over two decades trying to legalise it Bill to be debated on Tuesday night and Wednesday

Fourteen similar bills have been before the SA Parliament over the last two decades and all have failed, so what will be the fate of the 15th one?

Every vote is crucial, and this conscience vote is weighing heavily on the individual members of Parliament.

South Australian Liberal MP Duncan McFetridge introduced his Death With Dignity Bill on October 20, and with so much at stake, there are strong regulations attached.

Only a person with a terminal illness found to be suffering unbearable pain that cannot be relieved through other measures can make a request for voluntary euthanasia.

Their decision must also be endorsed by at least two doctors.

The bill will be subject to a conscience vote, but some MPs like Labor's Tung Ngo are already wishing the decision could be made for them.

"We're being paid big bucks to make this decision so it's very hard for someone like me and other members of Parliament to decide," he said.

"And sometimes I wish the faction and the party made that decision so we can hide behind that decision ... in this case, I'm still very undecided."

Liberal MP Michelle Lensink said it is a big decision. ( ABC: Angus Llewellyn )

Liberal MP Michelle Lensink said surveys always show consistently high support for voluntary euthanasia, and yet concern still sets in when people get into the detail.

"A lot of people will say, hypothetically, if I'm in a situation where I don't know what's going on and I don't have control of my body, I'd like to have voluntary euthanasia," she told Lateline.

"So it's also trying to work out, what do people mean by that?

"I think also people say things hypothetically — when they're in that actual situation is that really the choice that they'd make?"

John Darley said there is a lot of support either way. ( ABC: Angus Llewellyn )

Xenophon Team MP John Darley is no stranger to the voluntary euthanasia debate.

He said during his nine years in Parliament, the bill had come up about three or four times.

"There's a lot of support either way, but what I've found is that in speaking to people who would have been opposed to it, when they hear the sorts of safeguards that I'd need to have in the bill for my support, they basically come around to supporting it."

Some of the MPs find their personal situation weighs heavily on their decision.

Labor MP Tung Ngo is still undecided on how he will vote. ( ABC: Angus Llewellyn )

Labor's Tung Ngo was brought up in a Catholic family, and he said his default position would be against voluntary euthanasia.

"I believe life is precious and should be preserved and we should do whatever we can to save a life," he said.

"However, we have a situation where a question is being asked 'what happens if someone is terminally ill and in a lot of physical pain?'

"[It's] a very small percentage of our population, what should we do with those people?

"I've lost my dad beginning of the year through cancer and my mum in her very last moment in hospital with my dad would recite prayers to prepare his soul for his death.

"And I don't know what I can say or do if I decided to vote for voluntary euthanasia. I don't know whether I can tell her.

"I don't know whether she can tell her friends in the parish or the local priest and her brothers and sisters.

"So potentially they might say, 'I'm not your son, we thought you were proud of him'.



"Even with all my achievements, maybe it's come down to nothing.

"So it is a very difficult and very sad thing for me to have to decide."

'A quantum leap'

Mr McFetridge proposed legislation back in February but the bill copped criticism for allowing a person who did not have a terminal illness access to euthanasia.

"I've just got a feeling that if they come up with the right model, with their safeguards for vulnerable people, you might find people in the middle who swings toward and supports it," Mr Ngo said.

"But the question is they have to find that right model because the first bill that they put up got a lot of holes in there and they admitted to it, so now they came up with a new model."

There have been concerns from some MPs that controls on voluntary euthanasia could be relaxed once the practice was legalised.

For example, in some European countries, where euthanasia has been legal for some time, the legislation has been broadened since it was introduced.

"Because it is such a quantum leap, it's almost like once you've made this decision, is it ever going to be undone?" Ms Lensink asked.

"So that's a really big step for us to take."