Australian Peter Greste, Egyptian-Canadian Mohamed Fahmy and Egyptian Baher Mohamed of the satellite news broadcaster's English service were arrested in December 2013 in a case that triggered global outrage.
Greste and Fahmy each got seven years, and Mohamed was jailed for 10.
In June, the reporters, who authorities say lacked proper accreditation, were jailed for aiding the blacklisted Muslim Brotherhood and spreading "false information" after the army ousted Islamist president Mohamed Morsi in July 2013.
The Brotherhood, which saw great electoral success after the fall of long-time leader Hosni Mubarak in 2011, has since been declared a "terrorist organisation" in Egypt.
"The Court of Cassation could order a retrial, issue a new verdict or acquit the defendants," said Fahmy's defence lawyer Negad al-Borai, adding that the appeal could even be dismissed.
The three, who on Monday completed one year in prison, could also be freed on bail if a retrial is ordered, he said.
Australian Foreign Minister Julie Bishop on Monday downplayed speculation of a release, saying there had been mixed signals from Egyptian authorities.
Greste's parents told ABC in Australia they were hopeful the three would soon be released, saying they had "confidence in the integrity of the Egyptian appeals system".
Rallies in support of the three were held in London and The Hague on Monday.
Al-Jazeera's appeal cited "flaws in the arrest procedure" and "the fact that evidence presented in court did not marry with the charges".
The reporters were arrested when Egypt and the Gulf state of Qatar were at loggerheads after Morsi was removed by then army chief and now President Abdel Fattah al-Sisi following mass protests against his one-year rule.
Ties worsened when Qatar, a key backer of the Muslim Brotherhood, repeatedly denounced Sisi's overthrow of Morsi, and Cairo accused Al-Jazeera of biased coverage of the Islamist's ouster and the government crackdown that followed.
At least 1,400 people have died in the crackdown, mostly in August last year when police broke up two pro-Morsi protest camps in Cairo.
Thousands more have been jailed and dozens sentenced to death after often speedy mass trials.
"Their arrest was a settling of political scores between Egypt and Qatar," Borai said of the three journalists.
Thursday's hearing comes as ties between Qatar and Egypt improve following mediation by Saudi Arabia, a key Sisi backer.
Last month, Qatar joined its Gulf neighbours in supporting Egypt under Sisi in an attempt to end Doha's regional isolation over its backing for the Brotherhood.
And on 20 December, Cairo told a Qatari envoy it was ready for a "new era" with Doha, as the emirate offered its "full support" to Sisi.
Two days later, Al-Jazeera announced the surprise closure of its Egyptian channel, which had consistently criticised Cairo since Morsi's ouster.
"The warming of Cairo-Doha relations could be a consideration in influencing the judge's decision on Thursday," said Mustapha Kamel Al-Sayyid, professor of political science at the University of Cairo.
"No one can be sure, but it is quite likely the final result will be the release of the journalists. How and when that happens is another issue," H.A. Hellyer of the Centre for Middle East Policy at the Brookings Institution in Washington said.
Sisi himself has said he would have preferred the journalists had been deported rather than tried.
Greste and Fahmy were arrested at their makeshift office in a Cairo hotel where the authorities said they were working without mandatory accreditation.
The same court on Thursday will also examine appeals of four Egyptian co-defendants in the case, who were jailed for seven years for belonging to a "terrorist" organisation and for "damaging the image of Egypt".
Eleven other defendants tried in absentia, including one Dutch and two British journalists, were given 10-year sentences.
Source: AFP, via I-Net Bridge
For more than two decades, I-Net Bridge has been one of South Africa’s preferred electronic providers of innovative solutions, data of the highest calibre, reliable platforms and excellent supporting systems. Our products include workstations, web applications and data feeds packaged with in-depth news and powerful analytical tools empowering clients to make meaningful decisions.
We pride ourselves on our wide variety of in-house skills, encompassing multiple platforms and applications. These skills enable us to not only function as a first class facility, but also design, implement and support all our client needs at a level that confirms I-Net Bridge a leader in its field.
Go to: http://www.inet.co.za
