These following list of codes will only work on the European PAL version of the game.

Unlock ALL Weapons and Infinite Ammo:
If you're struggling with the game and feel you need more fire power to be able to reach the next level then press 'Start' and highlight Weapons and press Right + L2 + R2 + Square + Circle + X. You'll now have ALL the weapons in the game and an unlimited amount of ammo.

Unlock Stage Select:
If there is a particular stage you want to play then press 'Start' and choose Options. Then highlight 'Select Mission' and press Left + L1 + R1 + Select + Square + X.

Unlock Hard Mode:
If you want to play a more difficult version of the game then at the 'New Game' title screen press Left + L1 + R2 + Select + Square + Circle + X. If you have entered the code correctly Gabe will say 'Damn it!' as confirmation.

Unlock ALL Weapons and Unlimited Ammo in Current Level:
To enter this code pause gameplay and highlight the 'Weapons' option. Then hold Select + L1 + L2 + R2 + Circle + X.

Unlock Level Select:
During gameplay pause the game and select 'Options' and then highlight 'Select Mission'. If you now hold L1 + L2 + R1 + Square + Circle + X a list of ALL the levels in the game will appear.

One Hit kills:
During gameplay pause the game and highlight 'Objectives' and then hold Right + L1 + R1 + R2 + Circle + X. If you have entered the code correctly Gabe will say 'Understood' as confirmation.

One-Shot Kill:
During gameplay pause the game and highlight 'Silenced 9mm' and press Left + Select + Square + X + L1 + R2.

Unlock Super Ammunition:
During gameplay pause the game and highlight the 'Map' menu and press Right + R1 + R2 + X.

Unlock Weak Enemies:
During gameplay pause the game and highlight the 'Map' menu and press Right + L1 + R1 + X.

Unlock Hard Mode:
At the New Game title screen press Left + L1 + R2 + Select + Square + Circle + X.

Unlock ALL Weapons + Infinite Ammo:
During gameplay press 'Start' to pause the game then highlight Weapons and press Right + L2 + R2 + Square + Circle + X.

Unlock One-Shot Kill:
During gameplay press 'Start' to pause the game then highlight Silenced 9mm and press Left + Select + Square + X + L1 + R2.

Unlock Super Ammunition:
During gameplay press 'Start' to pause the game then highlight the map menu and press Right, R1, R2, X.

Unlock Weak Enemies:
During gameplay press 'Start' to pause the game then highlight Map and press Right + L1 + R1 + X.

Unlock Stage Select:
During gameplay press 'Start' to pause the game then choose Options. Highlight 'Select Mission' and press Left + L1 + R1 + Select + Square + X.