Oliver Curtis, former investment banker and husband of high-profile Sydney publicist Roxy Jacenko, cut a solitary figure as his lawyers challenged his conviction for conspiracy to commit insider trading.

The 31-year-old is serving a one-year jail sentence after a jury found him guilty on June 2 of striking an illegal deal in 2007 with his former best friend John Hartman to use inside information to bet in shifts in share prices.

The jury heard the old boys of St Ignatius' College, Riverview spent the $1.4 million profit on lavish living expenses, including a luxury holiday to Whistler and Las Vegas.

Curtis' father Nick Curtis, former Macquarie banker and resources millionaire, and mother Angela were in the NSW Court of Criminal Appeal on Wednesday to hear leading silk Bret Walker attack the Crown case against their son.

But Ms Jacenko, who made headlines in court during her husband's trial, did not make an appearance.

In documents filed in court, Curtis' legal team said the jury's verdict was "unreasonable or cannot be supported by the evidence".

Mr Walker told the court –  Justices Anthony Payne, Derek Price and David Davies –  that essential elements of the offence had not been proven.

He said the Crown had elected to prosecute Curtis with conspiracy to commit insider trading rather than the offence of insider trading itself, a strategy which had "advantages" or "virtues".

There was, however, also a "safety device" built into the offence of conspiracy.

"The agreement must be one which, if carried out, will result in the commission of an offence," Mr Walker said.

He said it was not enough that the agreement "may" result in an offence being carried out.

But Wendy Abraham, QC, for the Crown, said the agreement between Curtis and Mr Hartman was "very clear" and it was possible to be found guilty of conspiracy even if no offence could be carried out.

Ms Abraham said two or more people could "agree to possess an item they believe to be cocaine. [If] it's sugar, it's still a conspiracy."

"You can commit a conspiracy where the offence is impossible," Ms Abraham said.

She said it was not necessary to prove the "substantive offence" lying behind the conspiracy charge, although in this case those elements may also have been able to be proven.

Mr Walker said that, while an accused may believe they are receiving inside information, if it does not meet the legal definition of that term they "cannot, regardless of the wickedness in his or her heart, be guilty of an offence".

"You may be wicked but it's not an offence," Mr Walker said.

In this case, he said the jury could not have been satisfied the information the pair agreed Mr Hartman would pass on to Curtis – relating to Mr Hartman's trading intentions as an equities dealer at boutique investment firm Orion Asset Management – was in fact inside information.

The legal definition of inside information requires it to be material, meaning that if it were were freely available it "would, or would be likely to, influence persons who commonly acquire ... [certain] financial products" when deciding whether to buy or sell those products.

Mr Walker said the jury could not have been satisfied of "anything more than there may or may not have been materiality".

Justice Lucy McCallum sentenced Curtis on June 24 to a maximum of two years in prison but said he should be released after one year on a good behaviour bond.

In a strongly-worded judgment, she said it was "troubling that, unlike Mr Hartman, Mr Curtis has not embraced responsibility for his offending".

She said Curtis, who was working at boutique investment bank Transocean Group at the time of the offences in 2007 and 2008, had expressed "no contrition to any degree whatsoever" until after the jury found him guilty.

Mr Hartman, who the jury heard was caught "red-handed" by his broker in 2009, has already served 15 months behind bars after confessing to a string of insider trading offences, a small number of which related to the tips he passed on to Curtis.

He confessed and later cut a deal to reduce his jail time by giving evidence against Curtis.

The court reserved its decision.