The singlet and triplet potential energy surfaces for the reaction of HO 2 radical with Cl atom are explored by using high-level combination W1BD and W1U methods. Statistical rate theories are employed to compute the rate coefficients of the main product channels including HCl + O 2 ( 1 Σ u - ), HCl + O 2 ( 3 Σ g + ), OH + ClO and HOOCl as a function of pressure and temperature. It is found that the rate coefficients for the product channels OH + ClO and HOOCl are strongly depended on temperature and pressure. At lower pressures and higher temperatures, the product OH + ClO is important, while at higher pressures and lower temperatures, HOOCl is the dominant product. At some moderate temperatures and pressures, the rate coefficients for the formation of OH + ClO and HOOCl could be equal. The product channel HCl + O 2 ( 3 Σ g + ) proceeds via formation of a van der Waals complex Cl..HOO and, next, passes through a saddle point structure with a negative energy of − 5.0 kJ mol −1 relative to the reactants. It is shown that a two transition state model suitably describes the kinetics of this product channel.