Voltage Controlled Oscillators (VCOs) are a key element in PLL design. The simulation of VCOs is a time consuming process because transient circuit simulations must run long enough that the steady state is attained. Furthermore, the robustness of design against operating and technological conditions must also be tested by simulating the circuits at several corners, thus making the design methodology based in iterative simulation rather prohibitive for this class of circuits. The development of efficient and reliable VCO models is therefore a very important task, not only for the automation of the circuit design, but for design space exploration as well. Besides accuracy and simplicity, models must easily adapt to the rapid technology evolution. In order to grant such robustness, we must develop models based on transistor level technological parameters. This paper presents an accurate model for submicron Voltage Controlled Oscillators (VCOs). The model obtained is based on the Npower MOS model, yielding quite accurate results for sub micron technologies. An example considering a 1.2V TSMC013 VCO is presented, where the accuracy of the results obtained against Hspice simulation is shown. Results obtained in about 2 seconds have 4% average error, compared to simulations taking over 15 minutes.