The effects of gas pressure and gas component on the power transfer efficiency η and transition power threshold P th during the E–H mode transition in inductively coupled plasmas are studied. The evolutions of η during the E–H mode transition in pure Ar and Ar/O2 discharges are similar, i.e., in E-mode discharge, η slightly increases with raising the applied power (η is below 30%), whereas, an abruptly upward jump of nearly two to four times for η occurs when the discharge transits to H-mode, and then η monotonously increases with increasing the applied power. In addition, as the pressure rises, η increases rapidly first and then slowly in pure Ar discharge. However, η in Ar/O2 mixture gases discharge shows a non-monotonic behavior. It reveals a tendency of first increase at low pressures and then decreases at high pressures, which is because the resistive component of the plasma varies with the electron density n e and the electron effective collision frequency ν eff . Furthermore, a non-monotonic behavior of transition power threshold P th with the pressure is found, i.e., with increasing the pressure, P th first decreases and then increases. It may be caused by the threshold electron density, which is constant at low pressures (ν eff / ω < 1) but increases at high pressures (ν eff / ω > 1). [ABSTRACT FROM AUTHOR]