I think this is where I ask this question...I was told years ago that Oil companies made real oil cans that were empty for their displays because people where stealing the full display cans. My question is : how do you determine a reproduction from a real empty display can?

You basically answered your own question.....a "real empty display can" IS a real/original oil can, just unfilled and sealed with original lids.

tips on determining/spotting reproduction oil cans has been discussed at length on here....use the search engine and research the topic.
Darin