Thread three each shrimp and scallops alternately onto long skewers. Brush the seafood evenly with the vegetable oil. Sprinkle with salt and pepper. Reserve.
Blend the ketchup with the orange juice, maple syrup, Worcestershire sauce, vinegar, paprika and garlic. Preheat the grill to medium-high heat and grease lightly.
Brush kebobs all over with the maple-orange mixture. Grill for 2 to 3 minutes per side, basting often, or until shellfish turns opaque.