An option trading strategy which involves the expansion of a short call position as the price of the underlying increases. This strategy can be constructed by selling call options covered by a fraction of the underlying position (say 15%). If the underlying moves upward, the short calls may be bought back at a loss, and consequently higher-strike calls can be sold for a greater overall premium, covering a larger fraction of the underlying position (say 25%).

The process goes on in the same fashion, on the expectation that the price of the underlying would revert to its historical mean.