The gyrotron, a microwave tube capable of producing high power output at millimeter wavelengths, has recently found applications for electron cyclotron resonance heating of plasmas in controlled thermonuclear fusion reactor experiments. This paper describes work in progress at Varian Associates, Inc. to develop a gyrotron oscillator to deliver 200 kW CW at 60 GHz (\lambda = 5mm), more than doubling the frequency at which such devices are available. A pulsed oscillator which produced over 200 kw peak power is described. A CW oscillator is under construction. The latest experimental results are presented.