I'm 20 and I'm buying a Ford Mustang 2015?

I've been wondering how much it would cost to insure it and keeping it running at full potential? And also how much it would cost for the petrol monthly cost for everything?

Ultimately it all depends on which trim you are getting. If you are looking at getting the 5 liter v8 expect high insurance and high petrol costs. That is why I would suggest getting the v4 turbocharged ecoboost. It is expected to have very little cost of insurance and extremely easy on the petrol side with nearly 30 miles to the gallon on the highway. The v4 model will have slightly more power than even the v6 model at 315 hp versus the 300 hp v6. And will have more torque at 300 ft lb versus the 280 ft lb v6. Of course the V8 will beat bought at 435 hp and nearly 400 ft lb. But the v8 is not a suitable car for a 20 year especially in today's day and age due to high petrol prices and high insurance costs and danger in driving at such a young age. Get the v4 and you will really enjoy it. There's also the option of the 2016 Shelby gt350, but just like the 5 liter v8, it really only belongs to those people who are older, richer, and experienced.

Or Ford Shelby GT500

[insurance costs will be thru the roof. Ask your agent for estimates. The "full race" eco boost engines are just that. They won't get good mileage because your foot will always be to the floor. I can't believe they {eco boost] engines will be reliable daily drivers because of their complexity. Back in my day engines of this caliber were for dreaming only. The ecoboost 4 cylinder has more horsepower than the original boss 302. The mustang is a good choice but if I were you I would stick with the conventional v6. It has good horsepower with much less wear and tear on the engine and fewer moving parts. Your insurance co. Will live you.

All we can tell you is that insurance WILL NOT be cheap and gas costs will depend on what engine you get, how fast you drive, and how much it is at your local station.

So if you want to know about insurance premiums start shopping for insurance quotes or call your insurance company and ask them!

No, you're not buying a new Mustang kid.
Not if you have to ask about how much insurance and fuel costs.