The study of software engineering is advancing very much nowadays. Yet, a lot of mysteries are included in its different areas. This paper presents a brief study of the different phases of softwar development, emphasizing the software reliability considerations. To asses any advances in this field, one has to consider their impact on reliability. Therefore, some models have been developed to provide quantitative evalvation of soft-ware reliability. This paper presents three of the most important software reliability models, focusing on their statistical evaluation. Interesting practical results are obtained and comparison of these results is discussed.