This research depends on treating different waste polystyrenes like; general purpose polystyrene, foamed polystyrene (styropor), high impact, and rubber modified polystyrene (HIPS) by thermal cracking in order to have liquid products which might be used as additives to gasoline. These products are essentially aromatics and aromatic olefines of a high octane number > ١٠٠, free from sulfer and lead, and they are able to be used as octane boosters. It is possible to redistill these products in order to have styene monomer with a yield of ٤٠ - ٤٣٪, which can be used after that for polymerisation purposes.