We present electron collision strengths and their thermally averaged values for the nebular forbidden lines of the astronomically abundant doubly ionized oxygen ion, O^2+^, in an intermediate coupling scheme using the Breit-Pauli relativistic terms as implemented in an R-MATRIX atomic scattering code. We use several atomic targets for the R-MATRIX scattering calculations including one with 72 atomic terms. We also compare with new results obtained using the 20 intermediate coupling frame transformation method. We find spectroscopically significant differences against a recent Breit-Pauli calculation for the excitation of the [OIII] {lambda}4363 transition but confirm the results of earlier calculations.