National Research Council Canada (NRC) was commissioned by Transport Canada (TC) to gather any evidence that movement of liquid in a rail tank car could contribute or is contributing in any way to derailments of trains carrying liquid dangerous goods. A literature review was performed to determine the state-of-the-art in sloshing research and identify gaps in existing research related to tank car sloshing. Over 70 references were examined. A variety of applications were covered by the review including rail transport, road vehicles, aerospace and marine transport. Representatives from companies that load or ship liquid dangerous goods were consulted to determine if liquid dangerous goods are shipped in partially filled cars, and, if they are, what the typical frequency of partial-fill shipments is and what the typical fill level is. Canadian accident and incident data from the Transportation Safety Board of Canada (TSB) were reviewed to determine if sloshing has ever been mentioned or suspected as a contributing factor in an incident. Individuals from TC, TSB, United States Federal Railroad Administration, Association of American Railroads, and the rail industry were consulted to determine if unreported evidence of sloshing had occurred in the past. Analytical work was conducted to study the effect of tank car sloshing on derailment risk. A multibody dynamics (MBD) liquid sloshing model was developed for a railway tank car with formulas generated based on available Finite Element Analysis data. The new liquid sloshing model was integrated into an empty tank car MBD simulation model developed in 2009-12 to study the impact of curvature on track geometry safety standards. The ability of the empty tank car model to predict wheel forces accurately in curves was validated previously on more than 523 miles of track with 1,340 curves. The integration of the liquid sloshing model and empty tank car model provided an MBD model capable of accurately predicting the dynamic behaviour of a tank car with a wide range of liquid payloads as it travelled over the field-test track. For comparison purposes, a solid-payload tank car model was developed by taking the validated empty tank car model and adding a non-moving payload located in the bottom of the tank. Hundreds of thousands of dynamic simulations were conducted for the tank car with liquid cargo at various fill ratios and with the equivalent solid cargo on more than 1,000 measured curves. The results show that under some conditions tank car sloshing could increase the risk of derailment. The detrimental effect of tank car sloshing on rail safety increases with the increase of outage, trailing tonnage, grade, car length difference, track curvature and train speed. It is recommended that further investigation be performed to improve the liquid-slosh model and develop a tool that can be used by regulators and railroads to develop improved guidelines on train marshalling practices.