Chess Openings Lab
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Alekhine Defense: O'Sullivan Gambit

The O'Sullivan Gambit is 1.e4 Nf6 2.e5 Nd5 3.d4 b5, where Black offers the b-pawn for queenside play. It is unsound: after 4.Bxb5 White is a pawn up with a lead in development, and Black has to rely on piece activity and tricks.

Moves
1.e4 Nf6 2.e5 Nd5 3.d4 b5
ECO
B03
Engine
+1.81 · a large advantage for White (Stockfish 17.1, depth 20)
Played
239 games in our lichess sample
White scores
42.7%

Key ideas for both sides

White

  • Take with 4.Bxb5; the bishop is active and Black has no quick way to win the pawn back.
  • After 4...c5 answer 5.c4, kicking the d5 knight, and meet 6...Nb4 with 7.Qd1 to stay solid.
  • Simple development with Nc3 or Nf3 also keeps an edge; avoid grabbing more pawns at the cost of the king.

Black

  • Strike with ...c5 to open the c-file and hit d4 while White's bishop is on b5.
  • Use ...Nb4 and ...Qc7 to aim at c2, the weak point if White's queen leaves d1.
  • Put a bishop on b7 to rake the long diagonal toward e4 and g2.

Plans and pawn structure

If White simply develops, the extra pawn should count, since Black's queenside is loose and the e5 pawn cramps f6 and d6. Black needs immediate activity: ...c5, ...Nb4 against c2, ...Bb7 and pressure on the long diagonal. White should keep the queen near home, castle quickly and use c4 to remove the d5 knight from its post. In the sample White scored only 42.7% here, so the tricks work at club level even though the engine disapproves.

What the engine plays from here

Stockfish 17.1 at depth 20 rates the position +1.81: a large advantage for White. Its three top choices for White:

  1. +1.81 4.Bxb5 c5 5.c4 cxd4 6.Qxd4 Nb4
  2. +1.25 4.Nc3 Nxc3 5.bxc3 Bb7 6.Nf3 a6
  3. +1.25 4.Nf3 a6 5.a4 b4 6.Ng5 e6

Pawns, from White's side.

How it scores on lichess

239 rated lichess games reached this position; White scored 42.7%.

1200–159952.9%
1600–199941.2%
2000 and up34.4%

Light: White wins. Grey: draws. Dark: Black wins. About the sample.

How to play against it

Take the pawn with 4.Bxb5 and develop. Do not let a knight land on c2: watch ...Nb4 and ...Qc7 combinations. Castle early and give the pawn back only if it kills Black's activity. If Black plays ...Bb7, keep e4 and g2 covered so the long diagonal stays closed.

Questions

What are the moves of the Alekhine Defense: O'Sullivan Gambit?

The Alekhine Defense: O'Sullivan Gambit starts 1.e4 Nf6 2.e5 Nd5 3.d4 b5. Its ECO code is B03.

Is the Alekhine Defense: O'Sullivan Gambit good for Black?

Stockfish 17.1 rates the position +1.81 at depth 20, which is a large advantage for White. In 239 lichess games from our sample, White scored 42.7%. An unsound gambit that still scores well at club level; White only needs to take the pawn, guard c2 and develop.

What is the main idea of the Alekhine Defense: O'Sullivan Gambit?

Black sacrifices the b-pawn to open lines on the queenside and distract White's light-squared bishop. The idea is quick ...c5 and ...Nb4 pressure, but with accurate play White keeps the extra pawn.

What should White play next?

The engine's first choice is Bxb5, with Nc3 and Nf3 close behind. 4.Bxb5 accepts the gift and develops a piece at the same time, leaving Black a pawn down without clear compensation.

Updated October 2026. Sources and method.