Welcome to FlyerTalk NoLimits. Both of the above posters are correct, with an asterisk. I believe that the Star Lounge policy is that you must be flying on a Star Alliance carrier. Therefore if you were booked on a CO ticket, and flying on the metal (i.e. a plane) with some other airlines name on the side like Eva Air or Virgin you would not necessarily be allowed into a lounge. Still, it never hurts to ask. For US and UA lounges, you have access regardless of which airline you fly.

See: http://www.staralliance.com/en/benef...access-policy/

Paid Lounge Membership Customers: Eligible Paid Lounge Membership Customers have access to any Star Alliance member carriers' owned Business Class lounges.
Eligible Paid Lounge Membership Customers include United Airlines Red Carpet Club, US Airways Club - Star Alliance Upgrade, Air Canada Maple Leaf Club – Worldwide and Continental Airlines Presidents Club.
Customer must present a valid eligible paid lounge membership card
Customer must also present a boarding card for a same day Star Alliance flight departing from the local airport.
Customer is entitled to one guest


2Except: UA Red Carpet Club members may only access US Airways Clubs when presenting a valid RCC card and a same day departing boarding card for a US operated flight, or when departing on an international Star carrier operated flight.

3Except: US Airways Club members may only access UA Red Carpet Clubs when presenting a valid USC card with the UA or Star logo and a same day departing boarding card for a UA operated flight, or when departing on an international Star carrier operated flight