New laboratory experiments on different types of lock-exchange particle-driven gravity currents advancing into a flume of fresh water are presented. These include purely saline currents, monodisperse particle-laden gravity currents with both fresh and saline interstitial fluid, and bidisperse particle-laden currents. For each case a simple box model is developed. These agree well with the experimental data. We find that particulate gravity currents with saline interstitial fluid flowing into ambient fresh fluid are best described using a Froude number of 0.52 in the box model (cf. Huppert & Simpson 1980). However, particulate gravity currents with fresh interstitial fluid are best described using a higher Froude number of 0.67. The change in Froude number reflects the different shape and structure associated with the different density of interstitial fluid. For all experiments, box models provide accurate predictions for up to twenty lock-lengths.