It is important to examine the differences between the OPIS and the W-L data. Table 1 compares
the distribution of brands in the OPIS and W-L datasets against the CEC census. Both the
OPIS and W-L data undersample minor brands and independents. However, the overall distribution
of brands in the W-L data is closer to a random sample as measured by the CEC census.
Although the OPIS dataset contains more stations, it omits some major brands (ARCO, Chevron,