Bergen plays 5 card majors,

1 NT almost forcing (opener may pass a 5-3-3-2, 11 count or so).

2/1 Game forcing so you don't need strong jump shifts.

His raises are: 1 M - 1 NT 2 m - 2 M : Weak 3 card raise. Note that in any sequence, responder promises exactly the number of trumps mentioned in this list.

• 3 M : 3 card limit raise.
• 1 M - 2 M : Constructive raise. (7-10, 3 trumps).
• 1 M - 2 NT : Jacoby forcing raise.
• 1 M - 3 C : 7-10, 4 trumps. (A traditional 1S-2S with 4 trumps).
• 1 M - 3 D : Limit raise with 4 trumps.
• 1 M - 3 M : 0-6, 4 card support.
• 1 M - 4 M : 0-6, 5 card support.
• 1 H - 2 S and 1 S - 3 H : Preemptive, 6 card H suit. (Or whatever else you agree).

The method is based on the Losing Trick count.

More details can be found in Volume 1 of Marty Bergen's book on bidding and in Larry Cohen's book on the Losing Trick count.