In a method of operating an organic light emitting display device, the organic light emitting display device including a red sub-pixel, a green sub-pixel, a blue sub-pixel and a white sub-pixel, the method includes: receiving input data; calculating an on-pixel ratio (OPR) representing a ratio of a driving amount of the input data to a maximum driving amount; adjusting at least one gamma voltage of a first gamma voltage for the red, green, and blue sub-pixels and a second gamma voltage for the white sub-pixel according to the calculated OPR; and displaying an image corresponding to the input data using the first and second gamma voltages.