I know that ppl have fanatical attachments to both oils, but which is really better? XD-3: 0W-30 viscosity Cheap ($3.75CAD/L) Excellent extended drain performance Available in 1L and 4L bottles, and probably 5gallon pails as well. Has a 0W-40 'sister' product. Contributes positively to the North American economy. Available in Canada only. CI-4 rating for diesels. GC: 0W-30 viscosity Expensive Dyed green Questionable extended drain performance. Imported from a far away overseas land at great expense. Available Canada/USA.