While not as labor intensive as some methods, frequent adjustment of the depth and purging the unit of collected product may be required. Pumping systems designed for product-only recovery have a higher initial cost but are also considerably more efficient. The wide variety of sizes gives them the ability to fit many applications, including monitoring wells, but they can be difficult to position and keep at the correct depth. Some units will leave a layer of free product as thick as 1 to 2 millimeters. It should also be considered that as with any system that relies on hydrophobic screens to separate water and product, efficiency is decreased as viscosity is increased.
Viscosity can also be a drawback when it comes to magnetically driven electric units.
Peristaltic units must rely on proper operation of the check valves to perform at efficient levels. Should water enter the unit, most product pumps will emulsify the mixture and make recovery much more difficult. When the product viscosity is relatively low and these units are properly set, they can be an efficient means of removing oil from a well. Continuous loop belt skimmers have an initial cost less than product pumping systems, but higher than bailers and slurpers. With all the system's equipment located at the wellhead, maintenance is relatively easy and inexpensive.