I have been using my HDFC Bank credit card for 18 months with a clean repayment history. How can I request a credit limit increase, and what factors does the bank consider?

Forex markup comparison: Amex = 3.5%, HDFC Infinia/Diners Black = 2.0%, Axis Atlas = 3.5% but with milestone fee waivers, ICICI Emeralde = 3.5%, Standard Chartered = 3.5%. If you travel more than twice a year, the math favours Infinia or Diners Black.