A rovibrational kinetic energy operator for a two-vector embedded reference frame is derived for general polyatomic molecules of arbitrary structure. New compact expressions for (T) over cap in terms of angular momentum and linear momentum vector operators are explicitly given for tri-, tetra-, and pentatomic molecules. The necessary actions for the evaluation of kinetic energy matrix elements in a standard rotation-angular basis are summarized. The structure of kinetic energy operators in the body-fixed formulation is explained with the help of Cartesian components of angular momentum and linear momentum vector operators. Kinetic energy operators for tetratomic molecules in a bisector embedded body-fixed formulation and for sequentially bonded pentatomic molecules are derived to show how to use our general result for diverse coordinate systems.