As it stands, Mr Gray holds a 3.3 per cent margin over the Liberal Party, with its candidate Donna Gordin again trying to reduce the margin, which she nearly halved at the 2010 poll.
If Ms Gordin was to defeat the Resources and Small Business Minister, it would be the first time a party other than Labor has held the seat since its inception in 1984.
Ms Gordin recorded a 2.65 per cent swing after preferences in 2010.
The party has pumped more resources into the campaign this year, with Opposition Leader Tony Abbott already visiting the seat several times.
Greens candidate Dawn Jecks will also have her third tilt at the seat after running in 2010 and 2007, while Australian Christians Party candidate Bob Burdett will recontest the seat after running in 2010.
Craig Lawrence will run as the Palmer United Party candidate.