The roasting process of coffee beans occurs at a high enough temp to destroy some of the caffeine molecules contained within coffee. So, contrary to expectation, light roast coffees have more caffeine than dark roast. Espresso has a high caffeine content (~150 mg) for its volume of liquid (~2 oz.), but less than a normal cup of coffee (~235mg in 12 oz.). Here’s a great list of common coffee drinks and their caffeine content: bit.ly/CaffeineList.