Related Clues:

• Heating choice
• Old U.S. gas brand
• Acronym formed from 'Standard Oil'
• 'Giovanna d'___' (Verdi opera)
• It doesn't react well
• Bygone sign on U.S. highways
• Preoperative delivery, once
• Letter opener?
• Natural gas ingredient
• Old Phillips 66 rival
• Petrol station choice
• Composition of an endangered layer
• Vegas sign
• Exxon alternative
• Cook, as clams