Pressure-dependent networks were constructed for α, β, and γ isobutanol radicals. Pressure-dependent rate coefficients for each network were obtained from the master equation at 20 temperatures from 180 K to 1500 K and 20 pressures from 0.01 bar to 100 bar. The reservoir state method was used to compute the phenomenological rate coefficients, 32 based on the implementation described in Allen et al.. However, since Eckart tunneling was used in this work, the method was modified slightly; the cutoff between Boltzmann-distributed reservoir and the excited states was taken at the energy where the microcanonical reaction rate was 1% of the rate at the transition state's zero-point energy. This allows the transition point between excited states and Boltzmann-distributed states to adjust with the amount of tunneling. The maximum energy separation was 2 kJ/mol with at least 200 energy grains per well. Lennard-Jones parameters of σ = 4.64 Å and = 318 cm -1 were calculated using the 1-D minimization method with γRO 2 and N 2 as a bath gas. Collisional energy transfer parameters of ∆E down = 250×(T /300 K) 0.85 cm -1 were used, a value that has been used for a similar system of 2-butanol radicals in helium. For the three barrierless entrance channels of R + O 2 , inverse Laplace transform (ILT) of analogous reaction rates was used to obtain k(E) from k(T ). For αR + O 2 , we used the high-pressure-limit rate of the analogous ethanol reaction, CH 3 CHOH + O 2 , from Zádor et al. Rates for oxygen addition to βR and γR were taken from the rate rules developed by Miyoshi for tertiary and primary additions, respectively. Pressure-dependent rates were fit at each temperature and pressure to Chebyshev polynomials. Thermodynamic parameters, pressure-dependent and high-pressure-limit rate coefficients are available in CHEMKIN II format in the ESI. †