Pretend-But-Perform mechanism (also called a Game of Pretension) is a revelation mechanism that allows players to declare their types freely but mandates players to act according to their declared types. Using a between subject design in a controlled laboratory environment, we are hoping to measure the effect of this mechanism on a Cournot duopoly. Theoretical predictions dictate that regulating a Cournot duoply by Pretend-but-Perform mechanism will result in an increase in social welfare. In this specific setting, subjects will make announcements about their production costs and in return the mechanism will force them to produce the amount predicted by Nash equilibrium given their cost declarations.