|The chess opening characterised by the moves 1.d4 Nf6 2.c4 c5 3.d5 b5 (in algebraic notation) is known as both the Benko Gambit and the Volga Gambit.|
The main line continues with the moves 4.cxb5 a6 5.bxa6 Bxa6 followed by Black fianchettoing the f8 bishop. Black´s compensation for the pawn takes several forms. White has an immediate problem with the f1 bishop, for instance: if he moves the e-pawn to oppose the bishop on a6, then Black will play ...Bxf1, and after recapturing with the king, White will have to spend time castling artificially with g3 and Kg2; while if the bishop is fianchettoed it will be in a rather passive position, hitting White´s own pawn on d5. Black also obtains good control of the a1-h8 diagonal and can exert pressure down the half-open a and b files. These are benefits which can last well into the endgame and so, unusually for a gambit, Black does not generally mind if queens are exchanged; indeed, such an exchange can often usefully remove the sting from a kingside attack by White.
Although the main line of the Benko is considered acceptable for White, there are various alternatives which avoid some of the problems entailed in the main line. The simplest is to just decline the gambit with 4.Nf3 or 4.a4. Another idea, which is popular at the Grandmaster level as of 2004, is to accept the pawn but then immediately give it back with 4.cxb5 a6 5.b6.
The gambit´s most notable practitioner has been its eponym, Pal Benko. Various other prominent players of a combative nature have employed it at some time or another, though few have made it their main defence to 1.d4.