Aeration may seem friendly in a cup of coffee or soda, but it's deadly for powertrain components. All forms of aeration (air bubbles, foam and dissolved air) are harmful, especially in the context of hydraulic and lubricating systems. Aeration is not a new phenomenon, but is a growing threat. Engine downsizing, higher combustion temperatures, turbocharging, extended oil drain intervals, high-speed electrified drivetrains and lower viscosity lubricants are all contributors to the phenomenon. As the industry drives towards greater efficiency, understanding, measuring and controlling aeration will be critical to the success of future powertrains. OEM test specifications for engine durability have been updated with a requirement to measure aeration. Many components and subassemblies are increasingly expected to resist aeration, with benchmarking and simulated aeration tests. Unlike most performance or durability tests, there are few aeration test standards or accepted practices to follow. This white paper explores the different types of oil aeration, how to measure it and how to simulate it for test purposes.