As a result of the changes that occurs the lubricant oil during their use, aged engine oils tend to differ in chemical and physical composition from virgin oil. We have chosen for study theses variations (changes) the oil that is the most sell in Algeria for cars with engine gasoline. For this investigation the oil was examined at different kilometres. A combination of oil acidity and deposit formation were used to follow the ageing. Our results were compared to standards, which helped us further refine our experiences to draw conclusions about the future for the waste oil collected.