Three surveys - timed to coincide with the one-year milestone before the poll on September 18, 2014 - showed a strong lead for the pro-UK camp.
l Ipsos MORI found 59% of those certain to vote were opposed to independence, compared with 31% in favour and 10% undecided.
l YouGov put support for the Union at 52%, with 32% backing independence, 13% unsure and 2% planning not to vote.
l A Progressive Scottish opinion poll found 59% said they would vote No, 27% supported Yes and 14% were undecided.
Each survey quizzed more than 1000 Scots voters and posed the question they will face next year: "Should Scotland be an independent country?"
They followed the results of one conducted for The Herald by TNS BRMB, which found nearly half of Scots were pessimistic about an independent Scotland's economic prospects. On the question of how the economy would fare if Scotland left the UK, 45% said it would perform worse, 23% better, 17% were unsure and 15% believed it would stay the same.
Blair McDougall, campaign director of Better Together, said the pro-UK group would "never take Scotland for granted".
He said: "When we see polls like those published today, we think about what we can do to reach out to the minority who don't agree with us, what we can do to convince them."
A spokesman for pro- independence Yes Scotland campaign said: "As we get closer to the referendum next year, the choice facing voters will become clearer.
A No vote means more unwelcome changes to Scottish society from a Westminster system that isn't working for Scotland, whereas a Yes puts our country's future in our own hands and that means we can choose to make Scotland's wealth and resources work better for the people living here, which will deliver higher standards of living and more opportunities for the people of Scotland."
Yesterday's polls all suggested the number of undecided voters was significantly lower than the 28% found in a TNS survey earlier this month.
In line with previous findings, Ipsos MORI found men were much more likely than women to vote Yes - 40% compared to 24% - while 64% of females plan to vote No compared with 54% of males. More women were also undecided, at 12% compared with 7%.
People living in the most deprived areas were almost twice as likely as those living in the most affluent areas to back a Yes vote, 42% compared with 22%.
More than two-thirds of SNP supporters (68%) intended to vote Yes, while 75% of Labour supporters, 80% of Liberal Democrat supporters and 98% of all Conservative supporters said they planned to vote No.
However the survey revealed fluidity, with the number of SNP supporters intending to vote Yes falling from 76% to 68%, and the proportion of Labour voters inten-ding to vote Yes doubling from 8% to 16% since June last year.
Christopher McLean, senior researcher at Ipsos MORI Scotland said: "Our latest poll suggests that neither side is currently able to shift public opinion. It is clear that the Scots who remain undecided will become increasingly important as we enter the final year. On the one hand, although the No vote retains a healthy lead, the Better Together campaign will need to do more to win over undecided voters if it is to win convincingly. On the other hand, with the Yes vote sticking around its historical average, Yes Scotland will need to do more to win over undecided voters if it is to gain the momentum needed."
l Deputy First Minister Nicola Sturgeon said the forthcoming White Paper on independence would set out a "very strong case" for the move following criticism of Alex Salmond's policies by his former head of policy Alex Bell.