Electrical conductivity sensors are often used to obtain measurements of small-scale fluctuations, or microstructure, in the ocean. In applications on towed instrument packages, they provide the only way to estimate temperature fluctuations on scales down to about 1 cm. A number of designs for the sensors have emerged in the last few years which address the major requirements of the instruments, namely, high spatial resolution and freedom from fouling. Five specific designs are compared on the basis of these design objectives, with the intent of identifying those which most successfully reach the goals. A dual-needle cell is found to have very high spatial resolution, and a surface-mounted planar sensor is found to be most immune to fouling. Other sensors, such as the conductivity cell used in the Neil Brown Instrument Systems CTD, art found to be less optimum in this application.