Gasification of 100 wt % polypropylene waste was carried out for this work. The main objective of this study was to compare the effectiveness of tar elimination by some additives in the gasifier bed with an inert bed. Dolomite and olivine were used as in-gasifier bed additives. Dolomite was more active than olivine when using the same amount in the gasifier bed (30 wt %). Tar content was reduced by 92% when dolomite was used, whereas the reduction of tar with olivine was 40% when compared with an inert bed. However, dolomite caused a few problems by plugging the gas cleaning devices because of the high amount of particulates; this did not happen with olivine. Therefore, olivine was used as the preferred gasifier bed material. The bed was then tested with 100 wt % olivine, which is a hard material. The results achieved were good and promising, obtaining from the gasifier a tar content of 2 g/nm(3) at the exit, with an L.H.V. of 6 MJ/Nm(3) and a gas yield of 6 Nm(3)/kg(daf).