APA (7th ed.) Citation

PennWell Publishing Company. (1999). Natural gas petroleum directory. PennWell.

Chicago Style (17th ed.) Citation

PennWell Publishing Company. Natural Gas Petroleum Directory. Houston: PennWell, 1999.

MLA (9th ed.) Citation

PennWell Publishing Company. Natural Gas Petroleum Directory. PennWell, 1999.

Warning: These citations may not always be 100% accurate.