Since performance of conventional linear prediction (LP) deteriorates in formant estimation of high-pitched voices, several all-pole modeling methods robust to F0 have been developed. This study compares five such previously known methods and proposes a new technique, Weighted Linear Prediction with Attenuated Main Excitation (WLP-AME). WLP-AME utilizes weighted linear prediction in which the square of the prediction error is multiplied with a weighting function that downgrades the contribution of the glottal source in the model optimization. Consequently, the resulting all-pole model is affected more by the vocal tract characteristics, which leads to more accurate formant estimates. By using synthetic vowels created with a physical modeling approach, the study shows that WLP-AME yields improved formant frequency estimates for high-pitched vowels in comparison to the previously known methods.