  We study the degeneracy of theoretical gravitational waveforms for binary
black hole mergers using an aligned-spin effective-one-body model. After
appropriate truncation, bandpassing, and matching, we identify regions in the
mass--spin parameter space containing waveforms similar to the template
proposed for GW150914, with masses $m_1 = 36^{+5}_{-4} M_\odot$ and $m_2 =
29^{+4}_{-4} M_\odot$, using the cross-correlation coefficient as a measure of
the similarity between waveforms. Remarkably high cross-correlations are found
across broad regions of parameter space. The associated uncertanties exceed
these from LIGO's Bayesian analysis considerably. We have shown that waveforms
with greatly increased masses, such as $m_1 = 70 M_\odot$ and $m_2 = 35
M_\odot$, and strong anti-aligned spins ($\chi_1=0.95$ and $\chi_2=-0.95$)
yield almost the same signal-to-noise ratio in the strain data for GW150914.
