Heavy truck rollover remains a primary factor in truck driver fatalities and injury. Roll stability control (RSC) and electronic stability control (ESC) are technologies that have been introduced to reduce the incidence of rollover in heavy truck crashes. This report provides an analysis of the real-world experience of a large for-hire company that introduced RSC into its fleet starting in 2004. The carrier provided a well-documented set of data on the operations of its truck-tractors, including both those equipped with RSC and those that did not have RSC installed. The purpose of the analysis is to determine the effect of RSC on the probability of rollover, as well as to identify other factors that either contribute to rollover or help reduce its incidence.This study presents results on the incidence of rollover both in terms of rollovers per 100 million miles traveled and the percentage of crashes that resulted in rollover. The effect on rollover of cargo loading, driver tenure at the company, driver age, type of operation (bulk, truckload, LTL, etc.), and other factors are examined.Recent hires had a 50% higher rollover rate than more experienced drivers; younger drivers had higher rollover rates than older drivers. Cargo loading and curved roads were both strongly associated with rollover. A statistical model was developed to estimate the separate effect of RSC, controlling for driver age, tenure, cargo loading, roadway curvature, and type of operation. The results showed that RSC reduced the probability of rollover by about 25%.