The invention discloses a probabilistic control in gas turbine tuning for power output-emissions parameters. According to embodiments of the invention, a system includes: a computing device configured to tune a set of gas turbines (GTs) by: commanding each GT to a base load level; commanding each GT to adjust a respective power output to match a nominal power output value, and subsequently measuring an actual emissions value for each GT; adjusting an operating condition of each GT based upon a difference between the respective measured actual emissions value and a nominal emissions value at the ambient condition; updating a pre-existing emissions model for each GT based upon the adjusted operating condition; running a set of operating conditions on each GT and measuring an updated emissions value; and refining the updated pre-existing emissions model based upon a difference between the updated emissions value and the updated pre-existing emissions model.