Here in the Las Vegas area the local natural gas company is Southwest Gas.

Their Las Vegas area offices are located at:
Las Vegas
6040 Badura Ave, Suite 110
Las Vegas, NV 89118
Located in the Beltway Business Park (adjacent to Starbucks and Port of Subs)

North Las Vegas
1374 W. Cheyenne # 107
North Las Vegas, NV 89030

Customer Service Phone Number:
877-860-6020

Emergency Number (if you smell gas) 1-800-447-5422

The following link will take you to Southwest Gas' Web Site.
You can also start, stop or move service online.

Southwest Gas