Oulu 99 RoboCup simulation team is a simple; rule-based client which aims to play as effective soccer as possible without requiring the use of complex artificial intelligence. The tactical decision making of the client is based on simple rules which are determined by the players position on the field and the locations of the other players and the ball. By adding a weighted random noise factor to rule-based decision; complex and variable game can be achieved although the basic rules are kept simple. This results in code clarity and efficiency. In addition; the system can be relatively easily enhanced to be; for example; an adaptive system by replacing the current weighted random choice; which has fixed weights; with some more versatile algorithm while the basic decision rules stay the same.