 Pumps that operate in the high vacuum ranges typically don't operate, or only operate inefficiently, at atmospheric pressures, whereas pumps that work efficiently at atmospheric pressure usually cannot produce a vacuum lower than approximately 1x10−3 torr.One consideration for choosing a roughing pump is whether the pump uses lubricating oil that's exposed to the vacuum.This concern of "hydrocarbon backstreaming" where pump oil as a gas makes its way into the vacuum chamber, has led to oil-free pump designs on the market.