How many credit card transactions were completed online in 2007?

Answer 1

From the Federal Reserve's 2007 Payments Study Press Release:

http://www.frbservices.org/files/communications/pdf/press/2007_payments_study_press_release.pdf

"Among the three main types of electronic payments, the annual use of debit cards increased by about 10 billion payments over the survey period to 25.3 billion payments in 2006. Debit cards now surpass credit cards as the most frequently used electronic payment type. Over the same period, automated clearinghouse (ACH) payments grew to 14.6 billion, an increase of almost 6 billion payments. Credit cards grew by almost 3 billion payments to 21.7 billion in 2006. "

Since this is a fairly mature market figure a growth rate in 2007 equal to 2006 grow rate of 13.8% and you get an decent estimate of 24.7 billion in 2007.