  High-precision line intensities are of great value in various applications,
such as greenhouse gas metrology, planetary atmospheric analysis, and trace gas
detection. Here we report simultaneous measurements of cavity-enhanced
absorption and dispersion spectroscopy of the prototype molecule
$^{12}$C$^{16}$O using the same optical resonant cavity. Nine lines were
measured in the R branch of the $v=3-0$ band. The absorption and dispersion
spectra were fitted separately with speed-dependent Voigt profiles, and the
line intensities obtained by the two methods agree within the experimental
uncertainty of about 1\textperthousand. The results demonstrate the feasibility
of SI-traceable molecular density measurements based on laser spectroscopy.
