All lubricated compressors send oil downstream. The quantity will depend on the type of compressor. In a rotary screw compressor, oil in the lines may be due to faulty separation equipment or a compressor oil level that's too high. Check the air/oil separation system and change the separator element if necessary. Also follow the manufacturer's recommendations for the proper oil level. In a reciprocating compressor, the force feed lubricator may be set at an excessive level. Follow the manufacturer's recommendation for proper feed rate. If oil carryover continues to be a problem, you may need to add a coalescing filter to your system.