I was noticing that even though Volaris is a Mexican carrier it has some aircraft registered in the United States of America. Does anybody know why? Any info would be much appreciated! 
The aircraft are probably registered to a US leasing company. The US n-numbers can be searched on the FAA site, which will indicate the registered owner/company.
Marty
Yup. Either leased or financed through a US company. It is fairly common around the world.
Volaris is an airline operating out of Mexico. It is owned by a multi-European stock and shareholder firm, who capitalised on the flights that Mexicana operated and had to close business due to lack of business management. So due to it’s business model it learned the lessons that Mexicana did not want to do, by leasing American company owned and certifiably maintained aircraft.