def METHOD_NAME(self):
    # Oxygen concentration (oxygen concentration is zero in the negative electrode)
    c_ox_n = pybamm.FullBroadcast(0, "negative electrode", "current collector")
    c_ox_s = pybamm.Variable(
        "Separator oxygen concentration [mol.m-3]",
        domain="separator",
        auxiliary_domains={"secondary": "current collector"},
    )
    c_ox_p = pybamm.Variable(
        "Positive oxygen concentration [mol.m-3]",
        domain="positive electrode",
        auxiliary_domains={"secondary": "current collector"},
    )
    c_ox_s_p = pybamm.concatenation(c_ox_s, c_ox_p)
    variables = {
        "Separator and positive electrode oxygen concentration [mol.m-3]": c_ox_s_p
    }
    variables.update(
        self._get_standard_concentration_variables(c_ox_n, c_ox_s, c_ox_p)
    )
    return variables