The temperature and pressure dependence of the addition reaction of ethyl methyl ketone (EMK) with H(O)over dot(2) radical has been calculated using the master equation method employing conventional transition state theory estimates for the microcartonical rate coefficients in the temperature range of 600-1600 K. Geometries, frequencies, and hindrance potentials were obtained at the B3LYP/6-311G(d,p) level of theory. A modified G3(MP2,CC) method has been used to calculate accurate electronic energies for all of the species involved in the reactions. The rigid-rotor harmonic oscillator approximation has been used for all of the vibrations except for the torsional degrees of freedom which are being treated as 1D hindered rotors. Asymmetric Eckart barriers were used to model tunneling effect in a one-dimensional reaction coordinate through saddle points. Our calculated results show that the four reaction channels forming 1-buten-2-ol + H(O)over dot(2) radical (R5), 2-buten-2-ol + H(O)over dot(2) radical (R10), acetic acid + ethylene + (O)over dotH radical (R13), and 2-methyl-2-oxetanol + (O)over dotH radical (R15) are the dominant channels. When the temperature is below 1000 K, the reaction RIS forming the cyclic ether, 2-methyl-2-oxetanol, is dominant while the reaction R13 forming acetic acid + ethylene + (O)over dotH radical becomes increasingly dominant at temperatures above 1000 K. The other two channels forming 1-buten-2-ol, 2-buten-2-ol, and H(O)over dot(2) radical are not dominant but are still important product channels over the whole temperature range investigated here. No pressure dependence has been found for the reaction channels forming 2-methyl-2-oxetanol + (O)over dotH radical and acetic acid + ethylene + (O)over dotH radical. A slightly negative pressure dependence has been found for the reaction channels producing the two butenols. Rate constants for the four important reaction channels at 1 atm (in cm(3) mol(-1) s(-1)) are k(RS) = 2.67 x 10(15) x T(-1.32)exp(-16637/T), k(R10) = 1.62 x 10(8) x T(0.57)exp(-13142/T), k(R13) = 2.29 x 10(17) x T(-1.66)exp(-18169/T), and k(R15) = 6.17 x 10(-2) x T(3.35)exp(-10136/T). A comparison of the total rate constants for the addition of HO2 center dot radical to EMK and that for H-atom abstraction by HO2 center dot radical from EMK has also been carried out. We find that the abstraction reaction channels are dominant over the entire temperature range of 600-1600 K.