Benko Gambit is a queens pawn opening that starts with 1.d4 Nf6 2.c4 c5 3.d5 b5. This opening is a sub-variation arising from the Benoni defense. Black sacrifices a pawn for a very long-term compensation of open a & b files and active pieces.
The main line goes 4.cxb5 a6 5.bxa6 and here, black has two major options.
Black can immediately capture 5…Bxa6. But the most popular move here is 5…g6. Black is not in a hurry to capture on a6. And as we will see, focusing on quick development gives black additional good options. So move 5…g6 is recommended.
After 6.Nc3 Bg7 white has two ways of development.
White plays 7.e4
After 7.e4, black can play 7…0-0. Here, black’s idea is to actually provoke 8.e5, which looks dangerous but actually turns out to be bad for white. For example 8.e5 Ng8 9.Nf3 d6 10.exd6 Nxd6 11.Be2 Nxa6 and white’s early central pawn advance proves to be premature. Black has well-developed pieces and a possibility of queenside attack in the spirit of Benko gambit.
So the main line is 8.Nf3 and here, black plays a very interesting move 8…Qa5!
Black is already threatening …Nxe4! And here a normal move like 9.Bd3 is a blunder due to 9…Nxd5! and black wins material. Notice the featured game Gelfand-Carlsen for the full game.
Notice that black would not have this kind of tactical option had he wasted a move on playing 5…Bxa6. So you see, in Benko gambit, black should focus on getting a quick attack to create most difficulties for his opponent.
Continuing the main line, after 9.Nd2 Bxa6 (Finally!) 10.Be2 Bxe2 11.Qxe2 Qa6 12.Qxa6 Nxa6 and black has good compensation for the pawn.
White plays 7.Nf3
Alternative to 7.e4 is the line 7.Nf3 Bg7 8.g3 Qa5 (threatening Ne4!) 9.Bd2 d6 10.Bg2 Nxa6 11.0-0 Qb6 12.Bc1 Bd7 and again black has achieved a good game out of the opening.
Black’s standard Benko gambit plan is to play Rfb8-Nb4 or Nc7-b5 and put pressure on the a2 and b2 pawns.
Notice that after 8…Qa5 white has to be always careful because natural moves like 9.Bg2 lead to 9…Ne4! and white loses material.
Other options for white
White has a few other options on move 5.
White can play 5.b6, giving back the pawn to keep the a file closed. After 5…Qxb6 6.Nc3 d6 7.e4 Black develops naturally.
White can play 5.e3, protecting the b5 pawn. And the main line here is 5…axb5 6.Bxb5 Qa5+ 7.Nc3 Bb7 8.Bd2 Qb6 and since the d5 pawn is weak, black can regain his sacrificed pawn soon.
White can play 5.f3, with the idea of e4. Here black goes 5…g6. We are not interested in regaining the pawn with 5…axb5. After 6.e4 Bg7 7.e5 Ng8 8.f4 d6 9.Nf3 Nd7 10.e6 fxe6 11.dxe6 Nb6 black is fine.
Finally White can entirely avoid 4.cxb5 by playing 4.Nf3. But black can simply continue his standard plan with 4…g6 with the idea of Bg7-0-0-d6 with a good game.
Benko gambit is a very tricky opening to face for white especially after Qa5. White is a pawn up for good, but black always has a good pressure with his strong piece activity. Black’s development is natural and easy with g6-Bg7-Qa5-d6-Nbd7 or Nxa6-Rfb8…etc, while white has to play his moves very carefully to avoid traps.