The St. Petersburg Variation is a variation of the Nimzo-Indian Defense, catalogued as ECO E43. The line runs 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3 b6 5. Bd3 Bb7 6. Nf3 O-O 7. O-O c5 8. Na4 cxd4 9. a3 Be7, reaching the position shown below after 18 half-moves.
Black holds the centre with pawns on d4, and one pawn capture is available, so the structure has not settled yet. Development is level at three minor pieces each, and Black is up a pawn of material. It is White to move after nine moves. Both kings have castled kingside, so play tends to shift to the centre and the opposite flank; Black has doubled pawns on the d-file.
On the Nimzo-Indian Defense generally: One of the most respected defenses to 1.d4. Black pins the knight and fights for central control.
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The St. Petersburg Variation goes 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3 b6 5. Bd3 Bb7 6. Nf3 O-O 7. O-O c5 8. Na4 cxd4 9. a3 Be7. It is a variation of the Nimzo-Indian Defense and is catalogued as ECO E43.
The St. Petersburg Variation is ECO E43. ECO codes group openings by their move order, so nearby codes cover closely related lines of the Nimzo-Indian Defense.
Stockfish evaluates the position after 1. d4 Nf6 2. c4 e6 3. Nc3 Bb4 4. e3 b6 5. Bd3 Bb7 6. Nf3 O-O 7. O-O c5 8. Na4 cxd4 9. a3 Be7 at +0.38 at depth 18, which is a slight pull for White, within normal opening margins. Engine evaluation is only a starting point — at club level the practical value of a line is mostly about whether you know its plans better than your opponent does.
Black holds the centre with pawns on d4, and one pawn capture is available, so the structure has not settled yet. Development is level at three minor pieces each, and Black is up a pawn of material. It is White to move. Both kings have castled kingside, so play tends to shift to the centre and the opposite flank; Black has doubled pawns on the d-file.