Relative contribution of individual effective nuclear reactions (forward minus reverse reaction; see text) to the total nuclear energy production at the bottom of the O-burning shell during O shell burning (upper panel), at the beginning of the C–O shell merger (central panel), and at the end of the C–O shell merger (lower panel). The blue bars represent processes that are dominated by the forward reaction and have a positive energy contribution, while the red bars represent processes that are dominated by the reverse reaction and have a negative energy contribution. The three panels include all the reactions having an absolute ε/ε_tot > 10⁻³ (see also Tables A.3, A.4, and A.5).