* Proper nouns are specific names of people, places, or things. They are capitalized.
* Common nouns are general names for people, places, or things. They are not capitalized unless they are part of a proper noun.
"Gasoline company" is a common noun phrase. It describes a general type of business. It's not a specific, named company.
Examples:
* Proper noun: ExxonMobil (a specific gasoline company)
* Common noun phrase: gasoline company (general term)
To make "gasoline company" a proper noun, you would need to add a specific name:
* ExxonMobil is a gasoline company. (ExxonMobil is a proper noun)
* The Shell gasoline company is located on Main Street. (Shell is a proper noun)