  We investigate the effect of interchain repulsive interaction on the pairing
symmetry competition in quasi-one-dimensional organic superconductors
(TMTSF)$_2$X by applying random phase approximation and quantum Monte Carlo
calculation to an extended Hubbard model. We find that interchain repulsive
interaction enhances the $2k_F$ charge fluctuations, thereby making the
possibility of spin-triplet $f$-wave pairing dominating over spin-singlet
d-wave pairing realistic.
