This issue of Light-Duty Vehicle MPG and Market Shares Report: Model Year 1989 reports the estimated sales-weighted fuel economies, sales, market shares, and other vehicle characteristics of automobiles and light trucks. The estimates are made on a make and model basis (e.g., Chevrolet is a make and Corsica is a model), from model year 1976 to model year 1989. Vehicle sales data are used as weighting factors in the sales-weighted estimation procedure. Thus, the estimates represent averages of the overall new vehicle fleet, reflecting the composition of the fleet. Highlights are provided on the trends in the vehicle characteristics from one model year to the next. Analyses are also made on fuel economy changes to determine what caused the changes. Both new automobile and new light truck fleets experienced fuel economy losses of 0.5 mpg from the previous model year, dropping to 28.0 mpg for automobiles and 20.2 mpg for light trucks. This is the first observed decline in fuel economy of new automobiles since model year 1983 and the largest decline since model year 1976. The main reason for the fuel economy decline in automobiles was that every automobile size class showed either losses or no change in theirmore » fuel economies. The fuel economy decline in light trucks was primarily due to the fact that two popular size classes, large pickup and small utility vehicle, both experienced losses in their fuel economies. Overall, the sales-weighted fuel economy of the entire light-duty vehicle fleet (automobiles and light trucks) dropped to 25.0 mpg, a reduction of 0.5 mpg from model year 1988. 9 refs., 32 figs., 50 tabs.« less