Three resonances, the 3:2 mean motion resonance, the Kozai resonance, and the 1:1 superresonance, are known to govern the stability of the motion of Pluto concurrently. In this work, we report an extensive numerical exploration of the 1:1 superresonance region in element space and the effects of the giant planets on this resonance. It is shown that the 1:1 superresonance region is narrower than those for the other two resonances and that it is a second-order resonance. We use the orbits of known Plutinos to investigate our result. None of these Plutinos is in the 1:1 superresonance. We also find that the Jovian planets, especially Jupiter, play important roles in concert in the superresonance.