The reaction pathway of coconut shell fast pyrolysis was studied by analysis of the transient evolution product profiles as a function of temperature, measured directly in the sample bed. Fast pyrolysis of coconut shell produced (i) pyrolysis liquid containing CH, CO, and COC bands, (ii) char with the absence of COH and CO suggesting that ether and carbonyl compounds were decomposed below 600 °C, and (iii) gaseous product majorly consisting of CO2. Increase the heating rate has a greater effect on increasing the yield of aliphatic and carbonyl compounds compared to that of aromatic compounds. The selectivity of the fast pyrolysis liquid was shifted from vinyl species to carbonyl species at temperatures between 500 and 615 °C. In situ IR study suggests that CO and CO2 were mainly produced from cracking of CH and CO bonds. Fast pyrolysis of D2O-saturated coconut shell showed that moisture in the biomass does not increase the H2 yield at high temperature and H2 is mainly produced from breaking of CH bonds.