Excess Baggage Fees when flying with multiple airlines

How are the excess baggage fees applied when you are flying with mutliple airlines? We will be flying out with American Airlines but at our first stop we will switch to Aer Lingus.  They said they have an agreement with them, so our luggage will go all the way thru without having to be rechecked.  However, I am wondering how the fees will apply.  Will both airlines charge us their fee or just one of them?

TIA!
melissa

I just flew with Virgin to JFK and then Delta domestically. I phoned both airlines and both confirmed that the second airline would honour the fees of the first. In my case, I paid Delta for my overweight suitcase, and Virgin did not charge me a second time.

Hope that helps.

If you have a thru ticket then the 1 excess charge will cover all the airlines.......

Did you book the flights through American, Aer Lingus, or both?  I flew to the US for Christmas, and booked through BMI; my MAN-ORD flight was with BMI, but my ORD-ATL flight was with a partner of theirs, United.  Coming back, I paid overage fees to United, they checked the bags through, and that was it.