A question every chess player faces once in a while is: how deep should prepare my openings. If you grab your opening books you will find many variations that go all the way up to move 20 or 30. This has always made me believe that to be well prepared, I should learn my openings up to move 20 on average. But now I think I have to question this assumption. Memorizing openings up to move 14 on average, should be enough!
How I can tell? Hans Ree has written a column in the NRC, (a dutch newspaper, so the article is alas in dutch) in which he gives the results of some research he did. He checked how many moves it took in every game of the current Russian championship, to reach a unique position. After the first two rounds the maximum number of moves to reach a unique position was 17, the minimum 9 and the average number of moves after which a unique position was reached was 14.
Of course the 12 games of the first two rounds are only a small number, and it would be better to take lets say 10 recent tournaments to get more reliable statistics. But I did a small test with my own games of the last year (OTB, slow time control). My average was 13! Try it out with your own games. Just to see if you can really expect to see some benefits of memorizing openings up to move 25 or more.