Petrov Defense, 8...Bg4 easy equality for Black? When I analyze the 8...Bg4 Petrov it always seems like Black gets an easy equality. For example:

Garry Kasparov - Patrick G. Wolff
New York/London simultaneous 1984

1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. d4 d5 6. Bd3 Be7 7. O-O Nc6 8.
Re1 Bg4 9. c4
   9. c3 f5 10. h3 
      (a) 10. Qb3 Rb8 11. Nfd2 Bh5 12. Nf1 (12. f3 Nxd2
13. Nxd2 O-O 14. Qc2) 12... O-O 13. Ne3 Nxf2 =
      (b) 10. Qc2 O-O 11. Nfd2 Bd6 =+
      (c) 10. Nbd2 O-O =
   10... Bh5 11. Qb3 Rb8 =
   9. Bxe4 dxe4 10. Rxe4 Bxf3 11.Qxf3 Nxd4 12. Qd3 Ne6 =
9... Nf6 10. cxd5 (10. Nc3 Bxf3 11. Qxf3 Nxd4 12.
Qg3 dxc4 13. Bxc4 O-O 14. Bg5=) 10... Bxf3 11. Qxf3 Qxd5 12. Qg3 !? (12. Qxd5
Nxd5 13. Nc3 Ndb4 14. Be4 Nxd4 15. Be3 Ndc2 16. a3 Nxa1 17. axb4 Nb3 18. Bd5
O-O 19. Bxb3 Bxb4 20. Rc1 $11) 12... Qxd4 13. Nc3 O-O =+


Kasparov ended up outplaying Wolff in the middlegame, but out of the opening Wolff was at least equal. All the other lines seem to quickly end in equality as well.

Is playing 3.d4 the only try for an advantage in the Petrov?
No, it is not "easy equality". It is "complex fight where Black has good chances for equality, with theoretical debate still going on".

Anyway, 3.d4 won't be the only try for an advantage in the Petrov. 3.Nxe5 is still the main field where White looks for advantage. He can deviate from this game Kasparov-Wolff in several ways, including 5.Qe2 (recently renewed by Carlsen and Kramnik), 5.Nc3 (the main try for an imbalanced position, see Karjakin-Caruana, 1-0, in this year's Candidate tournament), or later 8.c4 (a lot of heavy-weight fights involving Anand, Kramnik, Leko or Naiditsch in the 2000-decade).