I'm wondering what determines the currency that is shown and charged when booking flights on Delta.com. Is it the departure country, the IP address of the user when booking the flight, the charge card billing address, etc.?

I would like to book my flights in US dollars, charged to my USD AmEx that has a U.S. billing address. My flights originate in CPH, however, and I am usually making the reservation online from Denmark.

The last time I tried to book a flight, I was having tons of issues with the website, so I ended up on the phone with web services in Dallas. She was quoting me USD throughout our conversation, but then suddenly insisted she could only book the ticket in Danish kroner because the billing address on my AmEx at that time was my Danish address.

Now I want to use my AmEx that has my U.S. address as the billing address. I've entered it in my account with the US address at Delta.com, but I'm still being quoted fares only in Danish kroner. So I'm wondering if she was correct about the currency being determined by the billing address of the charge card.

If I call SMS, will they be able to book an itinerary originating in CPH in USD? Or will it again default to DKK due to originating departure city?

(The reason I want the charge to go through in USD is that I always lose $30-50 or more per ticket on the exchange rate, plus risk more in exchange loss should I have to cancel and be refunded.)

Susan