Cedar chips were pyrolysed continuously in a screw-conveyer reactor at 550 °C. The nascent volatiles that contained heavy oil (HO, b.p. > 350 °C) with a yield of 19 wt%-dry-cedar were isolated from the char and in-situ subjected to reforming in a fixed bed of char from the same cedar as above. The reforming was performed in three different modes; thermal cracking (TC), partial oxidation with air (PO) and steam reforming (SR). TC at 800 °C resulted in an HO yield of 0.26 wt%. It was shown that HO was converted into coke and light gas over the char while the coke and/or char were gasified with steam from inherent and pyrolytic waters. The char activity was gradually lost during TC due to coking-induced loss of micropores. Changing the mode from TC to PO decreased HO yield to 0.13 wt%, but it was found that O2 was consumed mainly by the gas-phase oxidation rather than the char gasification. On the other hand, increasing PO temperature up to 850 °C successfully decreased the HO yield as low as 0.01 wt%. SR at 800 °C gave a result very similar to PO at 850 °C. Enhancement of steam gasification of the char and/or coke by increasing temperature or steam concentration was thus necessarily for maintaining the char activity. O2 was minimally involved in the char gasification, but in practical reforming, it is indispensable to keep the char bed temperature high enough to keep rapid steam gasification of the char.