Traditionally, the objective in undertaking a generation expansion planning (GEP) process has been to minimize the expected sum of yearly discounted costs (incorporate i.e., construction costs, operating costs, salvage value, etc.). Now, the objective is to apply GEP to today's competitive electricity markets in order to maximize the profits of individual GENCOs (i.e., the revenues based on market prices and capital and operating costs) and minimize the impacts of competitors' conflicting objectives. This paper introduces a long-term expansion model for GENCOs operating in the deregulated electricity environment. The model considers uncertainty, generation capacity limits, and expansion rate and investment during the expansion period. Numerical examples are provided.