This paper presents a fully integrated enhanced swing Colpitts oscillator that operates from supply voltages below 4kT/q. Design equations considering the oscillation frequency and start-up conditions required for operation of the Colpitts oscillator are derived. The oscillator was built with a zero-VT transistor, due to its high drive capability at low voltages. Measurement results obtained for a prototype integrated in the IBM 130 nm technology demonstrated the operation of the oscillator with 86 mV of supply voltage.