Abstract: To compute controlled fusion problems, four nuclear reactions are conventionally used. In the paper, cross sections of many thermonuclear reactions between the lightest elements are compared. We show that, along with the traditional four reactions, a tangible contribution can be made by the reaction T + T → 2n + 4He. At low temperatures, the reactions D + p → γ + 3He and T + p → γ + 4He make a considerable contribution and it appears that the rest of the reactions can be neglected. For the outlined reactions, we perform a more thorough processing of the experimental data and construct high-order accurate approximations. The accuracy of finding the S-factor is 2–6% and that of the reaction rate is 3–4% for the new reactions. © 2020, Pleiades Publishing, Ltd.