The Benko Gambit (also known as the Volga gambit) has a paradoxical reputation among chess openings - despite the fact that Black sacrifices a pawn on move 3 after White's most solid opening move (1.d4), it has gained respect as a stable defense against which White can have severe trouble establishing an advantage. The opening moves are:
With this move black challenges White's strong pawn structure in the center, at the cost of losing a small amount of material. For a long time, the only main lines for White were to accept all pawns offered to him by Black, hang on to the material, and try to win the endgame. A typical line of this kind would begin:
Both sides have castled, and White has an extra pawn. In return for the pawn, Black has control of two semi-open files (a and b) and a magnificently powerful fianchettoed bishop on the g7 square. It has been discovered over many years of tournament play that, even if White manages to exchange pieces and reach an ending a pawn to the good, Black's initiative and positional advantage are so strong that such endings can be impossible to win. This is why the Benko gained the reputation, almost unique among gambit variations, for being a solid, drawish line.
More recently, several lines have surfaced by which White can attempt to gain an advantage, most of which involve returning the pawn to Black at an early stage, and instead concentrating on speedy development and pressure in Black's weakest area, the center of the board. One example:
5.f3 (The Dlugy variation) axb5
Black is forced to decide between trying to hold on to his pawn at a loss of time, or to let White capture it in a more advantageous manner than in the main line. This variation is very tactical, with White often pushing through the center very quickly in an attempt to overrun Black's position straight from the opening moves. This kind of approach is more typical of the modern style of play against the Benko, especially among players who are comfortable in unusual, sharp attacking positions.