Final answer:
A significant rise in compression readings during a wet compression test compared to a dry compression test usually indicates worn piston rings.
Step-by-step explanation:
When performing a dry compression test on a gasoline engine, if low compression readings significantly rise during a wet compression test, it typically indicates worn piston rings. The introduction of oil during a wet compression test helps to seal the space between the piston rings and cylinder walls, temporarily improving the compression. In contrast, issues like burnt valves, defective head gaskets, or worn valve guides would not show a significant improvement with the addition of oil, as these components are not sealed by the oil in the same manner.