Special instruments are sometimes required to detect an oil spill, especially if the slick is very thin or not clearly visible. For example, if a spill occurs at night, in ice, or among seaweeds, the oil slick must be detected and tracked using instruments onboard aircraft or satellites. This technology is known as remote sensing. There are also surface technologies available to detect and track oil slicks. In addition, samples of the oil must often be obtained and analyzed to determine the oil’s properties, its degree of weathering, its source, or its potential impact on the environment. This analysis as well as tracking and remote sensing technologies are discussed in this chapter.