Unrestricted second and fourth order Moller-Plesset perturbation theory (MP2 and MP4), density functional theory (B3LYP and BHandHLYP), coupled cluster (CCSD(T)), and quadratic configuration interaction (QCI) calculations have been performed using both the 6-311++G(d,p) and 6-311++G(2d,2p) basis sets, to study the OH hydrogen abstraction reaction from formic acid. A complex mechanism involving the formation of a very stable prereactive complex is proposed, and the rate coefficients are calculated over the temperature range 296-445 K, using classical transition state theory. The following expressions, in L mol(-1) s(-1), are obtained for the acidic, for the formyl, and for the overall temperature-dependent rate constants: k(I) = (1.37 0.40) x 10(7) exp[(786 +/- 87)/\T], k(II) = (5.93 +/- 1.39) x 10(8) exp[(-1036 +/- 72)/T], and k = (5.28 +/- 2.35) x 10(7) exp[(404 +/- 125)/T], respectively. An extremely large tunneling factor results for the acidic path, as a consequence of the presence of a high and narrow effective activation barrier. The contribution of the formyl path to the overall rate coefficient, as well as the magnitude of the tunneling effect, explain the observed non-Arrhenius behavior.