Best-selling novels like The Da Vinci Code are often chosen because of a word of mouth recommendation, a survey to mark World Book Day has revealed.
Author Louis de Berniere enjoyed a word of mouth success
Dan Brown's blockbuster tops the list of titles having an initially low print run, but eventually sell millions due to word getting around.
Thursday's World Book Day will encourage readers to tell their friends about a book they have enjoyed.
Author loyalty is another strong factor which helps books to succeed.
Other novels since 1997 which have become best-sellers on the strength of personal recommendations are Captain Corelli's Mandolin, Memoirs Of A Geisha and Mark Haddon's award-winning The Curious Incident Of The Dog In The Night-time.
Other factors which are said to influence readers' book choices are the synopsis on the back cover, the jacket design - but much fewer people are swayed by advertising campaigns.
WORD OF MOUTH BEST SELLERS
1 The Da Vinci Code - 2.2m
2 The Curious Incident Of The Dog In The Night-time - 1.5m
3 The Lovely Bones - 1.3m
4 Captain Corelli's Mandolin - 1.29m
5 Eats, Shoots And Leaves - 0.94m
6 No 1 Ladies' Detective Agency - 0.9m
7 Birdsong - 0.85m
8 Memoirs Of A Geisha - 0.67m
9 The Alchemist - 0.64m
10 Schott's Original Miscellany - 0.63m
Source: Nielsen Bookscan
John Bond, manager of HarperCollins' literary division said the findings were "fascinating".
"Publishers often stand accused of becoming ever more sophisticated and cynical in their pursuit of creating instant author brands, when ultimately it is as likely to be good old-fashioned personal recommendation that really sells," he said.
The World Book Day's campaign to encourage people to recommend their favourite books to family and friends includes the circulation of eight million postcards carrying the message "spread the word".
The World Book Day survey also asked for appropriate titles for Tony Blair to read ahead of an election campaign.
The most popular suggestion was Dale Carnegie's How To Win Friends And Influence People.
Similar reading material for Gordon Brown included If I Was Boss by Kes Gray and Machiavelli's The Prince.