Amcor, whose board raised concerns about the cartel in late 2004, is believed to be the mystery tenant behind a 6300-square-metre lease deal at the Vantage office building at 109 Burwood Road, Hawthorn.
Website carsales.com.au is also believed to be in talks for about 2600 sq m in the building.
This should please Gold Coast developer Bruce Tilley, whose company First State Developments built the 13,000 sq m building.
The $60 million project, on the former Vatmi site at the corner of Power Street, caused controversy when it was announced in September last year, because it was considered a risk to develop such a large building without any committed tenants.
Since then, office supply has been unable to keep up with tenant demand in Hawthorn. Rents have gone up and vacancies fallen.
Amcor spokesman John Murray said the group was still considering its office options, but declined to comment further until a lease was finalised.
Amcor is expected to vacate about 7000 sq m of Melbourne office space, including 2300 sq m at 679 Victoria Street, Abbotsford.
Amcor sold a former industrial site beside the Yarra River in Alphington to the Valad Property Group in September, in a deal worth about $13 million. GormanKelly director Rob Kelly is leasing Vantage with Colliers International director Rob Joyes. Both declined to comment on speculation about Amcor or carsales.com.au, saying neither was a "done deal".
Carsales.com.au recently moved staff from 810 Whitehorse Road, Box Hill, to its head office at 77 Atherton Road, Oakleigh. The company did not return calls from The Age.
Engineering company McConnell Dowell confirmed in July that it would lease 4460 sq m in the Vantage building, including naming rights.
Mr Kelly said companies that wanted to move to the "eastern suburbs belt" of Hawthorn and Camberwell needed to plan 18 months to two years ahead if they wanted A-grade office space.
"We are increasingly seeing tenants forced to stay renting existing premises because nothing appropriate is on the market when they start looking," Mr Kelly said.
Amcor has been granted conditional immunity from prosecution, in return for its co-operation with the Australian Competition and Consumer Commission over the price-fixing cartel.
Cartel victims are pursuing an $800 million class action against Amcor and Visy; Cadbury-Schweppes has also launched a $120 million damages claim against the companies for over-charging on packaging.