Benko Gambit (5. bxa6)

White fully accepts the Benko gambit.

5...Bxa6, taking the pawn immediately, is the most direct approach. From a6 the bishop pressures White's e-pawn: should they move it, e.g. 6. Nc3 d6 7. e4, Black is very happy to play 7...Bxf1 8. Kxf1 and prevent White from castling.

However, there is no urgency to recapture the pawn (Black has three attackers and can bring another with ...Qa5+).

5...g6 is most common at master level. There are at least two different reasons: firstly, Black develops their kingside and control of the long diagonal faster. Secondly, this gives Black flexibility to decide how to recapture depending on how White plays. If White plays with b2 & Bb2, and/or g3 & Bg2, Black may rather play ...Nxa5 and choose between ...Bb7 and ...Bf5.

5...e6 is a sideline. This Benoni-style move attacks the pawn on d5 before White has a chance to reinforce it with e4. 6. Nc3 exd5 7. Nxd5 Be7 8. Nxe7 Qxe7 ⩲. Eliminating the pawn frees the c6 square for Black's knight, the position is open and dynamic.

1. d4 Nf6 2. c4 c5 3. d5 b5 4. cxb5 a6 5. bxa6

Wikipedia has related information at Benko Gambit.

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.