With my Delta AMEX the last two statement periods after buying 5 or 6K savings bonds each time one or two days later my availible credit was reduced to zero.The first time two different CSR said I was over limit because payment I made a week earlier doesn't credit until the END of the statement period & I would be charged 29.00 for being over the limit! LOL Second time it happened the CSR could do simple math and realized I should have well over 1k availible wrote some comments with my account & availible credit was reinstated.Bottom line if you have a AMEX card you need to always carry another card!