The Petrov has a drawish reputation; however, it offers attacking opportunities for both sides, and a few lines are quite sharp.

The Petrov has been adopted by many of the world's leading players, including world champions Vasily Smyslov, Tigran Petrosian, Anatoly Karpov, and Vladimir Kramnik, along with grandmaster Fabiano Caruana and others.

The Encyclopaedia of Chess Openings codes for Petrov's Defence are C43 (for 3.d4) and C42 (for all other lines).

3.Nxe5 is more popular but they often lead to similar positions and "there is no clear reason to prefer one move over the other".

For instance, White can plan a quick Be3, Qd2, and 0-0-0, and play for a kingside attack, trusting that his doubled c-pawns will help protect his king, and that his initiative and attacking potential will offset the longterm disadvantage of having doubled pawns.

Viswanathan Anand resigned after only six moves after falling for this against Alonso Zapata at Biel in 1988.

[5] The Cochrane Gambit, 4.Nxf7, is labelled "speculative but entertaining" by Nick de Firmian in Modern Chess Openings (MCO) 14th edition.

He evaluates the position in Veselin Topalov–Vladimir Kramnik, Linares 1999 as offering chances for both sides after 4...Kxf7 5.Nc3 c5!?

[6] The Paulsen Variation, 4.Nc4, is labelled "ineffective" by de Firmian in MCO, but is occasionally seen at grandmaster level.

This was played in the World Chess Championship 2018 between Magnus Carlsen and Fabiano Caruana.

[7] 3...Nxe4, the Damiano Variation, has traditionally been regarded as an error, though it has occasionally been seen in recent grandmaster play.

!, recently dubbed the Stafford Gambit, is considered dubious, but it sets a number of traps, and in the early 2020s it became popular in online blitz and bullet games.

with d3-d4 to follow, and Black has insufficient compensation for the pawn, though White must still play carefully.

Black can capture either pawn; also possible is 3...d6, transposing into the Philidor Defence.

A long and complicated tactical sequence which has frequently been seen in master games is 3...Nxe4 4.Bd3 d5 5.Nxe5 Bd6 6.0-0 0-0 7.c4 Bxe5 8.dxe5 Nc6 9.cxd5 Qxd5 10.Qc2 Nb4 11.Bxe4 Nxc2 12.Bxd5 Bf5 13.g4 Bxg4 14.Be4 Nxa1 15.Bf4 f5 16.Bd5+ Kh8 17.Rc1 c6 18.Bg2 Rfd8 19.Nd2 (diagram) and White has the slightly better endgame after either 19...Rxd2 20.Bxd2 Rd8 21.Bc3 Rd1+ 22.Rxd1 Bxd1 or 19...h6 20.h4.