In a small bowl mix together the 1/4 cup oil, lemon juice, oregano, and some salt and pepper. Pour over the chicken and marinate several hours, or overnight. Dry the chicken well on paper towels and sprinkle with salt and pepper. Reserve the marinade.
Heat the remaining 2 tablespoons oil in the pressure cooker and brown on all sides as many chicken pieces as will comfortably fit at one time in the Cooker. Reserve on a warm platter. Pour off the fat and add to the pressure cooker the reserved marinade and the chicken stock. Close the lid and bring to pressure. Cook for the suggested time (5-8 minutes). Serve the chicken with the sauce spooned over it.