The CH stretching spectra of cyclopentene at 25 K in a molecular beam and at room temperature in a gas cell are measured and compared. These spectra are modeled with an Hamiltonian written in curvilinear coordinates and taking into account, in the adiabatic approximation, the coupling of the CH stretching vibrations with the puckering motion and the angle deformations by Fermi resonance. The curves of the vibrational energy calculated as a function of the puckering coordinate exhibit several crossings. From these crossing points, the vibrational energy can follow different ways. The probability of following one or the other way is discussed and determined from the fit of the two spectra. The presence of some stretching vibrations with an unexpected asymmetrical variation is experimentally evidenced. A correct reproduction of the experimental spectra is obtained.