In this paper, we present the development and testing of a balanced Zeeman spectroscopy method utilizing wavelength modulation for selective detection of paramagnetic molecules. We perform balanced detection via differential transmission measurement of right-handed circularly polarized and left-handed circularly polarized light and compare the performance of our system to the Faraday rotation spectroscopy technique. The method is tested using oxygen detection at 762 nm and can provide real-time oxygen or other paramagnetic species detection for a variety of applications.