Olympic revenge on the line at Australian Swimming Trials in ...

It's no secret that Australian women's swimming has extraordinary depth.

But the women's 200m free takes things to a whole new level.

The event is one of the most hotly contested events at this Australian Trials as Australia's best fight it out to not only make one of two individual spots, but earn a place in a relay team that should challenge for gold in Paris.

Headlined by world record holder Mollie O'Callaghan and defending Olympic champion Ariarne Titmus, the depth of the field is simply extraordinary.

"Our women's 200m is absolutely stacked," Shayna Jack, who qualified sixth-fastest said.

"It's a scary event to go into. 

"We've got so many amazing women in this event, we all know how much of a privilege it is to represent Australia in the 200 and also the 4x200, because we do have that world record.

"This morning everyone's just got to go for it."

Shayna Jack was part of the team that broke the 4x200m relay at the World Championships in 2023.(Getty Images: Quinn Rooney)

All four of the women that set the 4x200m freestyle relay world record of 7:37.50 at the 2023 World Championships: O'Callaghan, Jack, Titmus and Brianna Throssell were in action — and all made the final.

Lani Pallister, who swam in the heats ahead of that world record swim also booked her place in the final, although fellow heat swimmer Kiah Melverton was only fast enough for 12th.

"I have been a heat swimmer two World Champs in a row, and it sucks," Pallister, who qualified third-fastest, said after her heat swim on Wednesday morning.

"I understand the importance in playing a part and that sort of thing but I think there's a huge difference in having the opportunity to stand up in a final.

"It's one of Australia's most important events and I think it's an event that we have the opportunity to do really well in."

Also in the field were a further three women who won bronze in the 2020 Olympics in Leah Neale, Meg Harris and Tamsin Cook, with Harris qualifying seventh-fastest for Wednesday night's final.

That Olympic bronze medal, behind the USA and China, still rankles.

"I think everyone has probably thought about it every day since Tokyo," Pallister said.

"I know Dean [Boxall] has, the relay coach.

"I have full faith in him [to pick the right squad]."

Positively, Australia will likely be at full strength in Paris.

Only Maddie Wilson is missing of the world record-breaking Fukuoka team, after announcing her pregnancy at Christmas with fiancé, Australian cricketer Matt Short.

O'Callaghan, who qualified for the Olympic team in the 100m backstroke on Tuesday, said she was "very, very nervous" about the 200m free when she spoke to the media.

"There's a lot of pressure riding on this event, especially having the world record in it," she said.

Mollie O'Callaghan is the world record holder in the 200m free.(Getty Images: Quinn Rooney)

"Whatever happens, happens, I would really love to make the team on this event and do the best job that I can."

She appeared confident in leading out the first heat of the day, reeling in fast-starter 18-year-old Hannah Casey to qualify second fastest behind 400m world record holder Titmus, who comfortably won the second heat.

Jamie Perkins (fourth-fastest) and Brittany Castelluzzo (eighth-fastest) completed the qualifiers for tonight's final, which Jack said will be must-watch.

 "It's going to be red hot tonight," she said.