Heat peanut oil in a wok or large skillet over medium-high heat. Stir in the garlic, and cook until the edges begin to brown, about 20 seconds. Add the green beans; cook and stir until the green beans begin to soften, about 5 minutes. Stir in the sugar, oyster sauce, and soy sauce. Continue cooking and stirring for several minutes until the beans have attained the desired degree of tenderness.