Having been a major user for many years, the only downside to closed loop oil mist is the cost. Having said that, the payouts that I know about are between 6 months and 2 years. That is not bad considering that you can reduce bearing failures by as much as 90%. I know of one user in West Texas who achieved a 98% reduction; they are the ones who paid out the project in 6 months. As for the environmental aspect, if the mist density is correct, the pressure is correct, and the reclassifiers are properly sized, the mess around the equipment will be far less than those pumps which have sump lubrication. Oil mist requires only some minor maintenance about every 6 months. In between times, the operator need only to be concerned that the reservoir is filled and that there are no warning lights on.