Preheat the oven to 325 degrees F (165 degrees C). Grease a 2-quart casserole dish.
Heat oil in a large skillet over medium-high heat. Add celery and onion; stir until tender, about 5 minutes.
Mix in bread crumbs and parsley; remove from the heat. Stir in oysters, eggs, salt, poultry seasoning, thyme, and pepper. Add enough reserved oyster liquid to moisten mixture, stirring until well combined.
Transfer to the prepared casserole dish.
Bake in the preheated oven until the top is golden, and a knife inserted into the center comes out clean, about 45 minutes. Serve warm.
