The continued disruption in the delivery of environment-friendly CNG bus chassis by two leading manufacturers--Tata and Ashok Leyland--due to non-availability of gas cylinders is all set to derail the process of mass introduction of CNG fleet on city roads by the September 30 deadline, set by the Supreme Court. Giving this information here today, the Delhi Transport Minister, Mr. Parvez Hashmi, said DTC as well as the private manufacturers have not been receiving CNG chassis for the last one month due to non-availability of fuel cylinders to be fitted in these buses. Since the cylinders are not available and have to be imported, the two companies have placed orders in Dubai and New Zealand but ti will take time before the delivery is effected.