As RF IC design has become more prevalent and more demanding, the need for a more precise VCO phase noise model has arisen. For both MOS and bipolar VCO's new formulas are still being proposed to model the phase noise, which is a key factor for a precise oscillator. In this paper, a previous phase noise model for a bipolar VCO as presented in A. Tasic and W. A. Serdijn (2002) is refuted and the formulas developed for MOS VCO phase noise calculations based in J. J. Rael and A. Abidi (2000) are adapted to bipolar VCO. Then, the results are compared and some conclusions are drawn for the comparison of these oscillators