We have measured the gain peak energy of GaInAs quantum dot laser structures, relative to the absorption peak, as a function of injection. We have used a calculation to remove the effects of state filling in the inhomogeneous distribution and to estimate the carrier density in the dots. We have identified shifts, which we associate with many body effects, of up to 8 meV at room temperature at injection levels typical for laser operation of about 2.2 electrons per dot, producing a peak modal gain of 10 cm−1.