This is a powerpoint presentation on bio-carbon accounting for bio-oil co-processing. Because of the overlapping range in the stable C isotope compositions of fossil oils and biooils from C3-type feedstocks, it is widely thought that stable isotopes are not useful to track renewable carbon during co-production. In contrast, our study demonstrates the utility of stable isotopes to: ? capture a record of renewable carbon allocation between FCC products of co-processing ? record changes in carbon apportionments due to changes in reactor or feed temperature Stable isotope trends as a function of percent bio-oil in the feed are more pronounced when the ?<
sup>
13<
/sup>
C of the bio-oil endmember differs greatly from the VGO (i.e., it has a C4 biomass source?corn stover, switch grass, Miscanthus, sugarcane? versus a C3 biomass source? pine, wheat, rice, potato), but trends on the latter case are significant for endmember differences of just a few permil. The correlation between measured <
sup>
14<
/sup>
C and ?<
sup>
13<
/sup>
C may be useful as an alternative to carbon accounting, but the relationship must first be established for different bio-oil sources.