Possible Clues:

• Gas brand that's also a musical direction
• BP gas brand until 2013
• Bowed, to a cellist
• California-based oil company
• ''__ iris'' (Spanish rainbow)
• Name on California gas stations
• Counterpart of pizzicato, in music
• Bar Council pens instruction for one on the fiddle
• It's in the Shell game
• With a bow, in a pit