St. Petersburg Variation

The St. Petersburg Variation arises when Black meets the Rubinstein System, 4. e3, with 4...b6. Instead of castling or striking at the center with 4...c5, Black prepares ...Bb7, which brings another piece to bear on e4 alongside the f6-knight and the pin on c3. The light-squared bishop is not yet committed, so ...Ba6, aimed at c4, remains possible. The name should not be confused with the Leningrad Variation, 4. Bg5.

White's most common reply is 5. Bd3, which contests e4 directly. After 5...Bb7 6. Nf3, Black can occupy the square with 6...Ne4. The second choice, 5. Ne2, prepares to recapture on c3 with the knight and keep the pawn structure intact, and it has given White the best practical results. Black has several named answers to it. The Fischer Variation, 5...Ba6, hits c4 while the e2-knight blocks the f1-bishop. The American Variation is 5...Ne4. The Romanishin-Psakhis Variation, 5...c5 6. a3 Ba5, keeps the pin in place. The third common reply, 5. Nf3, scores comparatively well for Black. The engine assesses the starting position as roughly balanced.