Do you have any source for the 5% stat? I don't mistrust you, but it would be nice to "see it with my own eyes" to be confident enough to use it in conversations with others.
"In Europe, it is estimated that between 4–6% of oil and gas is used for producing plastics."
- British Plastics Federation
It varies from country to country, and in the USA natural gas is the primary input instead of oil. Some gas or oil could be consumed by the plant, not actually ending up in the final product.
https://oilprice.com/Energy/Energy-General/How-Much-Crude-Oi...