It is pointed out that the accidentally resonant charge-exchange reaction, O+ + H0 ⇄ O0 + H+, is an important mechanism for causing the loss of singly charged oxygen ions from oxygen-contaminated hydrogen plasmas. Results of a Monte Carlo simulation are presented which show that the fraction of oxygen lost because of charge exchange exceeds 1/3 when the parameters ne ∼ 1013 cm−3, nH0 ∼ 1011 cm−3 and Te ∼ 3 eV are attained. This process may be important in determining impurity losses from the edge plasmas of tokamaks.