In a medium saucepan or rice cooker, combine rice and water and cook until the rice is fluffy. Stir in rice vinegar, and set aside to cool.

In a separate bowl, stir together soy sauce, oyster sauce, and sugar until sugar is completely dissolved. Cut spam lengthwise into 9 slices, or to desired thickness, and marinate in sauce for 5 minutes.

In a large skillet, heat oil over medium high heat. Cook spam slices for two minutes per side, or until lightly browned. Using the spam container as a mold, or with slightly moistened hands, divide and shape rice into 9 mounds. Top each rice mound with a slice of spam and wrap nori around it, tucking the ends on the bottom side. Serve warm or at room temperature.