Vaseline Stain on a Rug?

That's a huge problem.
I haven't had that particular problem, but I think that maybe one of these might help.
1- There is a product available called Lestoil. I buy it in Houston at a regular grocery store in the cleaning products section. It cleans thru grease and tar on floors so maybe it will help your carpet.
2- One time I tried to get heavy duty machinery oil out of a baseball cap and I literally used everything in the house. Then I tried Safeguard soap and it literally melted the oil away. Scarey, especially since it's a soap for the skin.

3- There is a product called Citri Solve. It's an orange scented product that gets rid of things like adhesive on glass and even is gentle enough to get rid of adhesive on skin. My hormone patches always leave a really gross adhesive stain and this is gentle and does the trick.
I wonder if gasoline would help, but really I'd be afraid to use this in the house - bad idea.
Did you try paint remover? Or turpentine? I'd also ask someone at Home Depot or some kind of hardware store.
I'd also email the website of the manufacturer. Maybe Johnson and Johnson? I can't remember who makes petroleum jelly though.
I'd also use http://www.ask.com - just ask your question and they come up with answers or at least other places you can look.
Good luck.