The elastic differential electron cross section of ${\mathrm{CH}}_{3}$I molecules, state selected with an electrostatic hexapole and oriented in an electric field by the linear Stark effect, was measured as a function of the transferred momentum at electron energies of 700, 1000, and 1250 eV. The molecular-state ensemble was oriented with a preferential direction of the molecular symmetry axis parallel or antiparallel to the electron beam. By switching the orientation on and off, the orientation-dependent interference contribution M\ifmmode\bar\else\textasciimacron\fi{}, normalized to the differential cross section of unoriented molecules, was determined, independently of a model, for scattering angles of 4\ifmmode^\circ\else\textdegree\fi{}--15\ifmmode^\circ\else\textdegree\fi{}. The results, which can be divided into pure orientation and alignment parts, display different dependences on the electron energy and the degree of orientation. Model calculations based on the independent atom model (IAM) were carried out for the state mixture present in the scattering region. They reproduce the orientation contributions fairly well, but show some deviations for the stronger alignment contributions. Assuming the validity of the IAM, a Legendre expansion analysis was carried out to extract the leading Legendre moments characterizing the oriented molecular-state ensemble. \textcopyright{} 1996 The American Physical Society.