A long call option on an index where a trader can profit from a rise in the price of the underlying index with unlimited reward potential and limited risk. For example, consider a given index (like SPX) that is at 2000 and an investor who buys one March SPX 2100 call at $20 ($2,000). On expiration date, if the underlying index is standing at 2150, the cash received on exercise of the call will be: 50 points x $100, or $5,000. The net profit is, then: 5,000- 2,000= 3,000.