Benko Gambit

Black offers White the b pawn. Declining comes with disadvantages so White usually accepts it, at least for now.

If White accepts, 4. cxb5, Black offers the a-pawn, 4...a6. If 5. bxa6, Black's idea is that in compensation for the pawn (Black is down two, but can take back on a6 at a time of their choosing), Black gets strong pressure against White's queenside from two half-open files, an open diagonal for the bishop to control from g7, and a good pawn structure.

If White wishes to avoid the positions resulting from 4. cxb5 a6 5. bxa6, then usually they accept the first pawn and decline on turn five (e.g. 5. b6). However, White also has several ways to decline the gambit on turn four.

Generally, declining at this stage is suboptimal because it allows Black to play ...b4!, expanding on the queenside and controlling a3 and c3, where White's knight would like to develop. In practice, Black often leaves the tension between the b- and c-pawns to see if White will accept the invitation to transpose back into a Benko gambit accepted.

Defending the c-pawn with 4. b3!? is a positional mistake that weakens the long a1-h8 diagonal. It can soon lead to difficulties for White, e.g. 4...bxc4 5. bxc4 g6 6. Bb2 Bg7 (Black pressures the long diagonal) 7. Nc3? Na6 8. a3 (to restrict the knight) Rb8 9. Rb2 Rxb2 10. Rxb2 Nxd5 (threatening ...Bxc3+ winning the rook).

Defending the c-pawn with 4. Nf3 is the "main line" of the Benko gambit declined on turn four. This allows 4...b4, but more common is 4...g6 5. cxb4 and the position becomes very similar to the accepted lines.

4. a4 is the Sosonko variation for declining the Benko. Black cannot leave their b-pawn there and maintain the tension, so they are encouraged to either take into White (after 4...bxc4 White can get their knight out to 5. Nc3 and play e4. Black may be up a pawn, but it is weak and doubled while White's development is unimpeded) or play 4...b4, closing down the queenside (and White can play 5. Nd2 and e4 instead). The most critical line is 4...Qa5+.

4. e4?! is called the Hjørring Countergambit. White offers the e4 pawn. If Black is playing automatically, then 4...b4? or 4...bxc4? allows 5. e5, kicking the knight back to g8. Otherwise, 4...Nxe4 and White has a trap 5. Qc3, x-raying the rook through the knight and pawn. 5...Nf6? 6. d6 is a discovered attack on the rook, then after 6...Nc6□ 7. cxb5 Bb7 8. bxc6 and White is up a knight.

3...b5 and the continuation 4. cxb5 a6 was analysed in an article by Boris Argunov, published in a 1946 issue of Russian chess periodical Шахматы в СССР, Chess in the USSR. Argunov lived on a city on the River Volga which lent its name to the gambit.^[1][2]

The opening was popularised in the 1960s by Pal Benko, who wrote a book of analysis under the title The Benko Gambit.^[3]

For explanation of theory tables, see theory table and for notation, see algebraic notation..

1. d4 Nf6 2. c4 c5 3. d5 b5

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Wikipedia has related information at Benko Gambit

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