In light of projected growth in immigration of the expected differences in auto ownership behavior between immigrants and the U.S.-born population, and of the importance of accurately forecasting car ownership for transportation planning purposes, empirical research on modeling the relationships between the socioeconomic characteristics of the household (including immigrant status) and auto ownership levels is critical. The current research contributes by developing car ownership models that incorporate the immigrant characteristics (time period of entry and duration of stay) of household members. Data from 1990 and 2000 were used to develop ordered-probit models for car ownership for single-adult and couple households. For each household type, the results indicate that after several socioeconomic variables are controlled for, both the duration of stay and the time period of entry have significant impacts on the propensity for car ownership. Broadly, the findings from this study support the assimilation theory, which states that the differences in behavioral patterns between immigrants and the native-born diminish with increasing duration of stay of immigrants in a foreign land. At the same time, strong cohort effects were also found. Specifically, the more recent immigrants appear to have a greater inherent preference for car ownership and consequently might be assimilating (i.e., reaching the car ownership levels of the native-born) faster. Single-adult households also appear to assimilate faster compared with couple households.