T This lubricating oil analysis is conducted at PT X with the aim of reducing the cost of purchasing lubricating oil. The goal is to achieve maintenance efficiency for replacing diesel engine lubricants at PT X. The operational target is not being met optimally as per the predetermined target. Preventive maintenance has been carried out by replacing the lubricants according to the engine\\\'s working hours. Therefore, what needs to be done is to optimize the use of diesel engine lubricating oil by selecting the right type of lubricating oil. This is done by evaluating and analyzing the lubricating oil\\\'s performance through testing at a laboratory certified by the National Accreditation Committee (KAN). The choice of lubricating oil has been appropriate and has a time interval longer than the manual\\\'s instructions. This can help reduce maintenance costs without damaging the engine by lowering the quality levels of the lubricating oil. The lubricant testing is done by periodically taking samples of the lubricating oil, with testing conducted at each interval of the engine\\\'s working hours. The goal is to obtain test results for the lubricating oil according to standard parameters, with the aim of reducing maintenance and purchasing costs for the oil. The results of the lubricating oil analysis in the laboratory show that by lowering the quality levels, it can be used at PT X with a working time longer than the engine\\\'s manual.