Two-dimensional numerical investigations have been carried out to study the flow and energy transfer characteristics of flow past two inline circular cylinders with a downstream cylinder subjected to forced transverse oscillations. The effect of transverse oscillations of the downstream cylinder on unsteady wake characteristics as well as exchange of mechanical energy has been investigated. The dynamic effects, wake behavior, and mechanical energy exchange between the fluid and downstream cylinder have been studied elaborately for different combinations of amplitude, frequency, and inter-cylinder spacing. The oscillation frequency of the downstream cylinder has been varied in the range from 0.4 to 2.0 times the vortex shedding frequency behind a single stationary circular cylinder. Three different values of amplitude, viz., 0.1D, 0.3D, and 0.5D (D being the diameter of either cylinder), have been considered. The spacing between the cylinders (center-to-center distance) is also varied from 2D to 5D for each combination of amplitude and frequency and for fixed value of Reynolds number (Re) equal to 100. Results are presented in the form of vorticity contours, variation of lift and drag coefficients, their signals, and spectra. © 2018 by Begell House, Inc.