The No Vote could win by a nose in the Same Sex Marriage poll, according to Griffith University academics.
They used Twitter to analyse what the community was really saying and, despite most other polls reporting the Yes vote to be leading the race, believed only 49.1 percent of people are in favour of gay marriage.
Around 485,000 tweets were analysed.
Dr David Tuffley said they used the same algorithm that successfully predicted Donald Trump's shock presidential win, Brexit and the last Australian election.
"We think this is a pretty accurate figure because what people say online tends to be closer to what they really think compared to what they say to other people," said Dr Tuffley.