The pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the origin band of the + 2A′′ ← 1A′ transition of propene (C3H6) and perdeuterated propene (C3D6) have been recorded at high resolution, allowing for the partial resolution of the rotational structure. The analysis of the spectra in the realm of the orbital ionization model for rigid-rotor asymmetric-top molecules enabled the determination of the adiabatic ionization energy of propene and the rotational constants of C3H6+ and C3D6+. The tunneling splittings resulting from the hindered rotation of the methyl group could not be resolved, and the analysis was therefore carried out in the Cs molecular symmetry group. Angular momentum contributions of pπ, dπ, and dδ character were included in the single-center expansion describing the molecular orbital out of which ionization occurs, leading to the selection rules |ΔN| = |N+ − N′′| ≤ 2 and ΔKa = Ka+ − Ka′′ = ±1, ±2 and to photoelectron partial waves with angular momentum quantum number up to l = 3. The observation of a strong spectral feature associated with ΔKa = 0 indicates the importance of vibronic interactions.