The rod and piston in an air compressor need lubrication to keep from overheating. Some compressors use oil that must be properly maintained, while oilless compressors use a slick material coating to provide permanent lubrication. For most private users and indoor use, oilless is a better option due to cleaner, quieter operation, plus minimal maintenance requirements. Oil air compressors may be a better choice where higher RPMs/PSI are required, or for hot, humid working conditions where rust or corrosion could become problematic.