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A structure for guiding surface plasmon polaritons (SPPs) over millimeter distances with tight mode confinement is presented and analyzed in detail using the finite element method. The proposed long-range plasmonic waveguide consists of a dielectric ridge deposited on a narrow metal stripe supported by a dielectric buffer layer covering a low-index substrate. It is shown that such an asymmetric waveguide structure can be designed to support a long-range symmetric SPP mode, featuring a propagation length of ≈ 3.1 mm and lateral mode width of ≈ 1.6 μ m at telecom wavelengths of ~ 1.55 μm. Our analysis covers a broad spectrum of parameters: ridge dimensions, buffer layer parameters (refractive index and thickness), as well as metal stripe width, considering in detail the underlying mechanisms of SPP waveguiding in this configuration. The suggested configuration offers easy connection to electrodes enabling, e.g., thermo-optic or electro-optic control, and is technologically simple, making fabrication possible using only a few lithography steps. Additionally, a new figure of merit is introduced, which is related to a number of plasmonic components allowed for a given mode confinement and propagation loss, aiming thereby at the evaluation of the application potential of plasmonic waveguides.