Nielsen Database have within their database all books published and sold. (For prospective authnors with an ISBN it is very easy to register with Nielsen and for free. If you can't find out how, ask and I'll point you in the right direction.) They have produced a list of the best selling books for 2012. They said,
'It was a year dominated by an incredibly successful trilogy - confirmed today when the Nielsen data shows EL James' Fifty Shades of Grey trilogy occupying the top three places in the 2012 top 100 bestsellers list.
Collectively, the novel shifted 10,509,988 copies in the year to December 2012, above the 2,113,017 for another trilogy, Suzanne Collins' Hunger Games.'
The list can be found at - http://www.guardian.co.uk/news/datablog/2012/dec/28/top-100-bestselling-books-2012#data
Glyn