We report the effects of scan rate/electron dose on the secondary electron contrast in liquid systems, studied by Environmental Scanning Electron Microscopy (ESEM). Understanding the mechanisms for SE contrast is essential: previous observations of oil-water emulsions have revealed useful SE contrast between the dispersed and continuous phases, attributed to differences in the electronic structure of these molecular liquids. However, it has been found that large oil droplets for example, have a propensity to give SE contrast that can be inverted (relative to the continuous water phase) as a function of scan rate/electron dose, as shown in Figures 1 & 2. In the ‘grabbed’ image, Figure 1, the scan rate is a relatively rapid 2.1 frames/sec. and results in the expected image of oil droplets with lower SE signal intensity than the surrounding water phase. However, the intensity of the oil droplets changes dramatically when the scan rate is slowed, such that the droplets appear bright. Figure 2 shows the same region of sample as in Figure 1, but with image acquisition over 30 seconds. The same contrast inversion can occur at rapid scan rate if higher magnification is used. Effects such as this could result in ambiguous interpretation of ESEM images. However, useful information may be gathered as to the dielectric nature of the medium — a property related to molecular structure. We note that similar scan rate-dependent effects have been observed in ESEM studies of solid samples, although the mechanisms responsible have yet to be rigorously established.