The electronic spectrum of CuO has been studied extensively experimentally. In his review on the spectroscopy of the 3d transition metal oxides (Merer, 1989), Anthony Merer summarized the available experimental data for CuO, which encompassed over 20 publications. There have been 4 subsequent publications on CuO that have included: high resolution Fourier-Transform emission spectroscopy (FTS) (O’Brien et al., 1996), mm- and sub-mm microwave absorption spectroscopy (Steimle et al., 1997), moderate resolution laser induced fluorescence (LIF) spectroscopy (Jin et al., 2002), and high-resolution molecular beam LIF spectroscopy, both in the presence and absence of an external electric field (Zhuang et al., 2010). Despite this extensive study, analyses of spectra have been restricted to 63CuO, even though the natural abundance of 65Cu is significant (63Cu:65Cu is 69%:31%). Additionally, the Λ-doubling parameter for the X  2Πi state of CuO is assigned a negative sign in the FTS analysis, but is assigned a positive sign in the microwave and molecular beam LIF analyses. In this study, high resolution spectra for (0,0) and (1,1) bands of the [16.3] A 2Σ− – X 2Πi transition of CuO have been recorded using intracavity laser absorption spectroscopy (ILS). Features due to the (0,0) band of 65CuO were clearly identified in the spectra and included in the analysis. The CuO FTS spectrum was retrieved from the archive for the McMath-Pierce Solar Observatory at Kitt Peak, and several additional vibrational bands of the [7.7] Y 2Σ+ – X 2Πi transition of CuO were identified in the FTS data, including the (1,0), (0,0), and (0,1) bands of 65CuO. The ILS, FTS, microwave and molecular beam LIF data were simultaneously fit to a mass-independent Dunham type Hamiltonian using PGOPHER. In total, 13,019 observations were fit to 1 constrained and 46 floated parameters. The results of this simultaneous fit show a Cu-isotope dependent shift in electronic energy for the [7.7] Y 2Σ+ – X 2Πi and [16.3] A 2Σ− – X 2Πi transitions of CuO. The results also confirm that the sign of q in the X  2Πi ground state is negative. Potential energy curves were generated from the molecular constants obtained in the fit for the [7.7] Y 2Σ+ and X  2Πi states using the RKR method. These potential energy curves are significantly different and clearly indicate the Y and X state do not form a pure-precession pair.