Recent high resolution data from the vibronic bands in the S-1<--S-0 electronic transition in HCOOH were combined with UMP2 ab initio calculations to establish the torsion-wagging potential energy surface over θ=+/-90&DEG; for the torsional coordinate and α=+/-60&DEG; for the wagging angle for the S-1 electronic state. The separations between the c- and a/b-type band origins were used to establish a global maximum of 5275 cm(-1) for the torsion-wagging potential function. The stability of the structural conformers in the S-1 state was obtained from the vibrational intervals in the OH torsional progression that were fitted to the levels calculated from a two dimensional torsion-wagging vibrational model. The fitted potential surface revealed a pair of stable conformers with minima at θ=+68.08, α=+57.51 and θ=-68.08, α=-57.51 deg. A second pair of conformers with minima at θ=-48.50, α=+44.77 or θ=+48.50, α=-44.77 deg was found to be 1207 cm(-1) less stable and to be separated by a torsional saddle point of 1270 cm(-1) from the more stable conformers.