def compute_marginal_cost(vom: float, fuel_cost: float = 0., efficiency: float = 1.,
                          co2_content: float = 0., co2_cost: float = 0.) -> float:
    """
    Compute the cost of producing/transporting one unit of energy.

    Parameters
    ----------
    vom: float
        Variable operating costs (in currency/unit of electrical energy)
    fuel_cost: float (default: 0.)
        Cost of fuel (in currency/unit of thermal energy)
    efficiency: float (default: 1.)
        Percentage of electrical energy produced using one unit of thermal energy
    co2_content: float (default: 0.)
        Quantity of CO2 (in unit of mass) contained in one unit of thermal energy of fuel
    co2_cost: float (default: 0.)
        Cost of CO2 (in currency/unit of mass)

    Returns
    -------
    float
        Cost of one unit of electrical energy (in currency/unit of electrical energy)
    """
    return vom + (fuel_cost + co2_cost * co2_content) / efficiency