A large dataset of B3LYP energies and gradients that spans a large configurational space has been reported for C 14 H 30 . Two linear regression PIP fits to a dataset of 253,646 energies were reported. One uses a three-fragment approach consisting of 24, 23, and 23 atoms with a total polynomial order of 2. After removing duplicates, there are 14,739 terms in the PIP basis. This results in a modest linear algebra problem to determine the corresponding number of coefficients. The second approach is a many-body one, up to 4-b terms. This approach leads to a much small linear algebra problem to determine only 1227 coefficients. Both PESs produce precise fits and were shown to be robust for describing the torsional motion of this molecule and also for molecular dynamics calculations.