We are interested in learning how commercial intake valve detergents contribute to combustion chamber deposits (CCD) in modern vehicles run for higher mileage. It is appealing to use short mileage (<5,000 miles) tests to evaluate the CCD performance of gasoline. However, the ability to extrapolate CCD performance to higher mileage (≥10,000 miles) is uncertain because of changes in CCD formation processes. For this reason, CCD from base fuel and a commercial IVD detergent package were generated in duplicate 10,000 mile tests using four 1996 model-year vehicles. The detergent package used a polyalkylamine detergent combined with a synthetic carrier fluid and achieved 94% intake valve deposit (IVD) reduction averaged across the four vehicles tested. The CCD weights were found to be variable between repeat tests but, when pooled across the four vehicle fleet, the CCD weights were found to be statistically the same for both the additized fuel and the base fuel. The aromatic carbon, hydrogen and organic oxygen levels in the CCD were the same for base and additized fuel when pooled across the 4-car fleet and the chemical analysis results were virtually identical between repeat tests. These results indicate that changes in the CCD formation mechanism are not responsible for CCD weight variability between repeat tests. These results also indicate that little of the hydrocarbon components of the detergent and synthetic carrier fluid are incorporated into the CCD under the conditions of the 10,000 mile test. Higher nitrogen levels are measured in the CCD from additized fuel and the nitrogen-containing head group of the polyalkylamine detergent is the likely source for the higher nitrogen levels. Other engine tests using the same detergent/carrier fluid combination and treat rate (655 wppm) gave comparable IVD reductions and little or no change in CCD weights or chemical compositions relative to base fuel. In contrast, a similar polyalkylamine detergent combined with a mineral oil carrier fluid (1,373 wppm), decreased IVD but increased CCD and altered the deposit's chemical composition relative to base fuel.