As a step towards a complete CMOS avalanche photodiode imager, various avalanche photodiodes have been integrated in a commercially available CMOS process. In this paper, design considerations are discussed and experimental results are compared for a wide variety of diodes. The largest restriction is that no process change is allowed. Even with such a restriction, gains of more than 1000 at an incident wavelength of 637 nm using 83 V for one diode type and 45 V for another one has been shown. Thus, the feasibility of CMOS compatible avalanche photodiodes has been proved, allowing us to proceed towards the next step of integrating controlling circuits, readout circuits and avalanche photodiodes on the same chip. Further developments in this area is already in progress.